I'm going into this as a video gamer, not as a D&Der. IOW, this isn't in relation to D&D rules, it's just how I think Mages would work better implemented in the BG computer game.
I never liked the "chance to learn a spell" mechanic, and I still don't think it's implemented correctly, but I never go by it anyway. I typically save up my scrolls, then set the difficulty to Normal and scribe everything, then set it back to whatever I was using.
Here is how I would like to see INT implemented for Mages. Instead of giving you a higher chance to learn spells, it should have an impact on casting itself.
I think it should have an impact on saving throws. I'd do it something like:
Level - Saving throw bonus
1-4 : +3
5-7 : +2
8-9 : +1
10-15 : +0
16-17 : -1
18-19 : -2
20-22 : -3
23-24 : -4
25 : -5
You could tweak the numbers one way or the other I'm sure, but I'd like to see something like that. This would make INT actually meaningful and also make things like potion of Genius actually cool.
This would also apply to SORCERERS, and would thus make INT meaningful for them, as it should be.
It would also makes Gnomes much more attractive, since with a tome of INT you would be able to get -3 to savings throws with Gnomes (on top of -2 for Illusions).
Ideally, to do this you would first add 1 to the base saving throw modifiers of every spell, so that castes with 16-17 INT would basically have the same saving throw mods that they currently do, while casters with 18 INT would be 1 better than current.