For me character progression is pretty important (by character progression i mean exactly that, the character, exluding armor,weapons and such). Becoming better yourself, at playing the game is also a big part for me, but to be able to improve your character more adds alot, even if it just a little, and it can be a variety of things really, to feel your character has improved. You are correct that even if I reach the limit this will probably not make me stop playing if the game is good, I guess it really can be called secondary (the progression). Setting yourself goals as "I will kill this boss under 10 minutes" or "I will reach level 5 for less then 1 hour" can be fun and may help you become a better player, but this is to a degree cause by progressing to the complete end in the game world.
At some point I do want my character to be very strong and be able to hande most things relatively easy, but still be possible to get beaten by something very weaker than you if you make a mistake/underestimate that weak opponent. I want to be able to become incredibly powerful being but keeping some balance of course and "realism". As i said even someone incredibly strong can lose to an inferior enemy, anything can happen in fight.
I just don't want to have cap that is too limited. In some games i always look for mods or ways to unlock the level cap or skill cap(maybe), but I never abuse such things. ;D And I love the focus to make the game in a way that you are not thinking about the most effeciant way to level up or something like that, to be ready to kill and do anything if it gives alot of xp or currency. When I play i act as i would in reality and in reality there is infinire room to better your self and progress, so the best thing for me would be to have a sort of limitless progression, but this is limited by alot of things in a game such as balance, resources, mechanics and more. ;D
As I said above the information that was just given about the caps and thaumaturgy, and everything, sounds awesome to me and I have nothing to complain about, it is exactly the opposite. ;D