The score for "next level" after level 40 is of course incredibly high, so is that the end of leveling up, or is there a decent way of ever reaching that score (i.e. without playing the game through about 10000000000 times)?

Yes, it is possible to go above level 40, but you will have to go through a lot of hassle. Try using the invulnerability/level warp cheat and turn invulnerability on and first warp to the hall of rememberance, save, then beat Onyx Golem, then warp to Ice Cave Level 3 and beat the ice dragon there. You'll get a good amount of experience from those 2 battles alone! Repeat the process over and over again. Once you unlock extreme difficulty, fight those same 2 battles on extreme difficulty and you'll get even more experience. But, you'll need to start a new game in order to fight them again!

So anyone ever make it to level 41?

Maybe if you keep raising your Wisdom using the level 20 cheat code over and over, your experience will go up fast enough to do it?

if any of you botherd to look in the manual it tells you that lvl 40 is maximum

No it doesn't, Whitey.

I have the manual right in front of me, and nowhere does it say the maximum level is 40.

Plus, you continue gaining experience after level 40. What makes it very difficult is that the experience for level 41 is very high.