Don't misunderstand me. I really like RCT 1 + 2, and I have loved it since they were released. But I really think, that the parks are easy. I know, that in RCT 2, you can make more challenging maps. But the problem with RCT 2 is also, that you really not can achieve anything by completing parks, like in RCT 1, there a completed park unlocks a new.
In RCT, especially parks in vanilla and Added Attraction are very easy, and quite monotonous. Loopy Landscapes added a little more challenge and variety. But there were still easy. It is not unusual, that I can complete a park with double as many guest, as the task say. The only challenge is only, if a rollercoaster crash a month before deadline, and park rating drop below 600. Otherwise, I use a lot of time on waiting to reach the deadline.

So why not set yourself arbitrary challenges? Complete the scenario without building a roller coaster, or without removing and trees, etc. Triple the number of guests. Find something you DO find challenging and focus on that.

I'm with you on the monotony thing, though. I'm playing through for the second time and I'm finding it really annoying/boring having to wait out the clock.

That sounds like a good idea. I'll do that. I've never think about that before.

For RCT2 there is the wonderful UCES pack, a bundle of additional scenarios that are in many aspects more thoughtfully made than what came with the original game. No idea if you find them harder, approached with only the scenario goal in mind they might not be. But they sure lead to making more beautiful or interesting parks besides the default "delete all thats there, slap down favorites 1-17, wait"

In case you never downloaded additional stuff: Like all scenarios and saves that contain new objects, rct2 will crash the very first time you try to load each of them. Don't worry, it will work afterwards, some game glitch about importing things.

Thanks very much for that link! The scenarios looks awesome!
And yes, the official maps in RCT2 was quite poor. Many of them looks like maps made by a (in best case) mediocre map-maker. No shit, one of the official map (Extreme Heights) was just a random use of the mountain tool, and a coaster. And that's it!
But how old are this unofficial expansion pack?