Perhaps, but if so, it'll be a very, very long time before I reach that point...and my history with video games says I probably won't get there at all. And in the meantime, when in some of these dungeon areas I've got to deal with a dozen or more enemies attacking from various directions and ranges -- some through floors and walls -- all while avoiding those damn spiked balls (and occasional spike walls/floors/ceilings). It is, as you say, great for gathering loot & materials, but my equipment isn't yet at the point where I can just wade through rooms full of these guys with impunity.
Not that it isn't kind of fun, for a while, picking off hordes of baddies with a barrage of water bolts; the problem is that, unlike a Blood Moon or a Goblin Invasion, the waves of enemies never stop coming -- not until you leave. I suppose I could move the water candles (some, at least) somewhere else where they wouldn't be such a hindrance, but that would probably be dangerous and/or time-consuming in and of itself.
But, yeah, it is nice that many, if not most, of these negative things can be re-purposed for positive uses sooner or later. That's one of the reasons I eventually decided to buy the game -- I could tell it was one of those games that would have a lot of "emergent gameplay" situations.

Oh, I think its a great idea to harvest those water candles. The dungeon drops aren't worth bothering with.

Carry one around, and put it in your killing ground for blood moons and especially solar eclipses. Farm those broken swords. Might get lucky with a Death Sickle, too...

Normal mode drops in the Dungeon aren't all that useful outside Nazar (1% chance from Cursed Skull) which you need for the Ankh (and thus the Ankh Shield).

But the hardmode drops are useful, if only to help you fight the harder bosses the first couple of times (until you get the currently best items). Wisp is a great light source, Magnet Sphere, Shadowbeam Staff and Inferno Fork are all great spells that only get eclipsed by the rewards for the currently hardest content. The Rocket Launcher is a great mining tool with the right rockets (and proper safe distance being observed). Ectoplasm is the basis of the (arguably) best mage armor in the game.

Oh, right. For hardmode, I'd much rather pick the place I want the battle, put in a mess of traps, then place a candle or 2 (so I can move some) and drink a battle potion, rather than having higher number of fights where I'm at a disadvantage.

I still dick around in this game occasionally, though mostly just exploration and compulsive mineral-mining (even ones I will likely never use much more of, like tin) and monster-hunting.

Here is a horribly out-of-date shot of my spelunking progress. I've since explored most of the sky, and have expanded several of the cave networks on the map quite a bit, too. (This is a small world, by the way.)

Here's a more up-to-date screenie of my exploration progress so far in my (small) main world. Still haven't started really exploring Hell yet, and I'm honestly not sure I even want to bring Hardmode to this world. Then again, I'm getting bored just exploring, I'm not really a collector, and I haven't gotten into building weird, wild stuff just for fun, so I might have to try Hardmode just to bring some challenge back to the game. That, or start fishing. (In-game, I mean. :) )

Honestly, I don't consider a Terraria game to be really "started" until I enter hardmode. Everything up until that point is prepwork. The real game doesn't start until afterwards. It's not just difficulty that's added, there's quite a bit of content as well. The great variety of fun magical weapons is reason alone.

Fishing crates can contain hardmode ores (or bars) if you open them in a hardmode world, so if you're thinking about taking up fishing, save the iron and gold ones until after the Wall of Flesh. They can also be used as an alternative ore source to breaking altars if you're paranoid about the corruption or hallow taking over your world.

If you build four barriers 5 blocks wide at the edges of the "V" that forms after the Wall of Flesh is defeated (just 5 blocks of empty space works fine) and get your ores from boxes, you never have to bother with the Clentaminator.

Having 2 King Slimes spawn in a row is pretty lucky. It has only spawned a few times during my playthroughs. The summoning item is pretty "expensive" to craft which is why I don't summon it manually very often.

With the 1.3 update to come out tomorrow I'm pretty excited, curious to see what Expert Mode will be like and what it will be like to get the Expert Mode only items.

Forgot to post about it right after it happened, but a while back, I wound up doing an all-(in-game)-night Eye of Cthulhu serial killing spree. I was always curious how many times I could kill the bugger in one night; right now, my personal best is 7 or 8 times in a row. (As I said, I forgot to write anything down about it at the time, so I don't recall the exact number, but I had 8 or 9 suspicious-looking eyeballs in my piggy bank beforehand, and only one left when dawn broke.) Also, for the first time since I've been attempting this, I killed every one I summoned -- none of them ran away with the coming of the day! =) The weapons I used weren't anything special: basically, water bolts and a space gun. (Was wearing the meteorite armor, or whatever it's called, so the laser gun didn't require any mana; I'd shoot water bolts till out of mana, then switch to the gun till my mana refilled.)

Anyone else attempt such things? I don't mean farming bosses or other monsters for materials or item drops, but just seeing how many times you can kill a certain boss in a certain period, or trying to kill every boss with a certain type of weapon, that kind of thing. Self-imposed combat challenges, I guess. =)

With certain setups and specific bosses, it's possible to deal enough damage to kill them in one or two attacks. However this is due to those bosses consisting of multiple parts and requires those parts to be lined up correctly while using an attack that pierces all of them. Highest amount of damage would probably be falling from the very top of the world to the very bottom and then being Stoned by a Medusa with enough duration for you to land. Being Stoned increases fall damage and prevents any of the Immunity to Fall Damage accessories from working. I'm 99% certain that the Portal Gun doesn't carry over any fall height.

Without cheating it is currently impossible to heal more than 599 HP from a single effect. This requires a full compliment of Heartstones (granting 400 HP), Life Fruit (+100 HP) and an active Lifeforce Potion (+20% HP), being at 1 HP while talking to the Nurse for healing. You'd need a decent timing to achieve this since you regenerate health outside combat (and you have to survive with just 1 HP left). Once you trigger hardmode, a v shape with one line being corruption and the other hallow will be released from the bottom center of the world. 3 bosses will be hard/impossible to fight in space due to their mechanics. Another 2 will enrage (extra speed, damage and armor) and murder you asap due to taking them out of their biome. Bases are quite possible in the space biome, just look out for Wyverns in hardmode.

The question I'm getting at is this: When this happens, can the new corruption overwrite hallow (and vice versa)?

The newly spawned corruption (or crimson if that's the type of world you have) / hallow from triggering hardmode will override whatever biome was there before if possible. This only affects grass (on dirt), stone, sand, and ice (including the corrupt/crimson/hallow versions of course).

This brings up a different challenge: Construct a world in such a way that triggering hardmode will fail to spawn any corruption/crimson or hallow, then trigger hardmode.

Wondering how long it would take to do this, and whether the game has any contingency to ensure that some coruption/crimson/hallow gets spawned.

Okay so I made it so that it rains my house all of the time.

I don't know why I did that.

But I did. :D