lw2jgog: 10% isn't /that/ huge, but it's nice. I gather that there are a couple of training dummies in Act III, but that's a bit late.
Off-hand, Cover, Assassin, Strong Stomach, and Haggle also have very limited windows of opportunity, so if you're restarting, be sure to nail those as well.
Syvere: Will I get to 35 without it is my main concern? What's off-hand? I have those others. Didn't know about experienced until today. Goddamnit...
Depends on the path you choose. On one you'll get to 35 quite easily, on the other you might not even reach the cap with experienced.
Keep in mind that certain levels of progress throughout the game have their own level caps - so, once you hit one of those you won't level up with experienced either until you get further along. I guess experienced doesn't make a huge difference in the end result, but rather makes you hit the partial level caps a bit faster.
On perks generally: They're nice to have, and some of them even are quite a big advantage, but none of them are necessary for the game to be fun or to beat it. In my opinion, a missed perk just isn't worth starting all over.