Isn't there an infernal warping point for getting sin-confidence, though?
If I remember correctly, the confidence for sins required a steadily increasing level of sin... So while a modest character might get a point for bragging a proud character wouldn't get any for declaring himself Gods equal. (sin of pride)
we took the opposite approach - we never "gave out*" Xp, all Xp came from study (or Practice) whether for magi, companions or grogs. (We also used the "average XP per year" to advance the bulk of grogs). We dealt with XP in the downtime between sessions (usually at the very start, very end, or by e-mail between).
(*in exceptional circumstances, some characters' players chose to take Adventure XP for the season, rather than count study time.)
Why did we do this?
Because Ars Magica is a game about the (fast) passage of time, with the characters moving through whole seasons at a time. A couple of days adventuring mid-season is neither here-nor-there, just an interlude. The passage of 1 day is of little significance to a character - it takes time and repetition to alter (improve).
As for roleplaying ... perhaps we play in an utterly different style to your group?
We never had a question about whether or not one was playing a role... the very fact that (adventure) actions did not accumulate XP meant that players were freed to let their characters behave as they wanted, and no need to worry about gaining XP. Magi tried to stay in their labs, but were often winkled our by circumstance, protesting, and playing up to their flaws until forced to use their powers to sort things out...