I most certainly want to be able to level up the sovereign the way i see fit! He is my Avatar in the game, a surrogate me, if i want to train (put points in) strength or spellcasting or whatever and the game would not let me because of autoleveling, this would irk me very strongly and interfere with my suspension of disbelief - a sure way to become desinterested in a game. The cost could and should be different for casters/warriors/summoners - in this i agree with vieuxchat, but the possibility should be there.
Heroes i could live with autoleveling - they are hired/recruited help after all, although i would like to be able to control some aspects - i actually think spellforce 2 was kinda on the right track about this, there were some heroes who were very set in their (autoleveling) ways, some allowed decisions every second lvl, some were yours to develop just like your main char. There should also certainly be perks to pick up along the (leveling) way, something to develop, with prerequisites and synergies to keep things interesting. I am pretty sure that for a lot of people, myself included, the character development is a very important part of the game, and i would really like to significantly change my avatar from playthrough to playthrough. To be the ultimate summoner once, pyromancer in the next game, master swordsman in another. A lot of people want to have customisable alter egos from sims through neverwinter nights to jagged alliance there are a lot of evidence of it.