Fairly simple, but fairly handy change.
When using any of the 1-3 "Steal spell" abilities provided on yourself, instead of getting the "You are unable to steal spells from yourself!" message instead give a quick rundown of the spells you have stolen, in which slots and what the next DC of that spell is (so you have an idea if you can cast it again after the next attempt)
Just a nice and easy way to keep an idea of which spells you know are in which slot and how much use you're likely to get out of it.
A tool to see what spells you have already would make sense. Beyond that however, I don't see the most powerful support 'class' receiving anything more as desirable.
I'd like to resurrect this suggestion. I often encounter the annoyance of forgetting which spells I've got memorized in which slot! I don't know how difficult this would be to implement, however.
Clearly, if you forgot what spells you memorized, you no longer have them memorized. You might consider leeching new ones instead.
I'm attempting humor.