Yah the armorclass has always worked fine for me too. Although I am thinking of expanding it from 500 to -500 or 1000 to -1000. I have 100 player levels and for them right around level 30 to 50 they start to already have -300 ac often with spell ups and such, and anything after -300 is Moot. Although I could alter my code of armor type objects so game wide they would offer less protection, but that causes players to complain when they see their stats lessen. It's easier just to expand.
That is true in the short term, but in the long term leads to HP counts in the millions, gold counts so large they don't fit into integers, and so forth. Sometimes it might be better to rein things in earlier rather than later; the longer you wait the harder it becomes both in terms of the work you have to do and the effect it will have on the players.
Ware! Ware! Here be the path to Ye Olde Monty Hall Gaming, and the Way of the Twink!
There's almost NOTHING I hate more than seeing games with gigantic numbers all over the place. It reminds me of those old pinball games where the last two or three digits were just painted on, because everything was a multiple of 100 or 1000 to make people feel like they didn't suck because they scored 307,000 points. They only scored 307 points, but that sounds wimpy to someone playing the easy machine out front.
I've always been of the opinion that a level should be an achievement. You should sit back and go "Woah!" when you finally gain enough experience to level. If you expand your game from 20 to 40 levels, do you really want 40 levels? Or are you just giving in to the whining players who want to see levels come twice as fast? I used to laugh at many of the newer muds that cropped up back when WileyMUD was running, because their level 100 was far easier to get than our level 20.
Personally, with 100 levels and AC ranges of -1000 to 1000, I'd be tempted to just divide every single number in the game by 10 and call it good while you work on the new expanded levels 11 through 15. *grin*
I've always been of the opinion that a level should be an achievement.
It's all a matter of personal taste; personally I dislike the very concept of levels, preferring the more granular advancement of a levelless system.
However a well designed game should have both long-term and short-term goals. If you want levels to be long-term goals then you should aim to have relatively few of them, while if you want levels to be short-term goals then you'll want a larger number of them.
Neither approach is inherently better or worse than the other, although taking it too far in either extreme will reduce the appeal of your game (much as I enjoyed playing a mud ~13 years ago which had only 3 levels).