What would be the best use of my time in private meetings with agents if the agents are not good matches for me personally? Normally I would just ask for feedback on my query regardless but I think my query's already working (8 of about 40 queries requested a full or partial).I'm not sure why you're participating in pitch sessions, or one on one sessions, with agents who aren't a good fit for your work. Surely you can ask to be re-assigned to another agent if a conference organizer made the matches. Or just not use the appointment and give it to someone who needs it.
Not good matches= they have rejected my first book and don't rep the genre of my current book (well one does but specifically says "don't send me books about X" and mine is about X). Would it be uncouth to (politely) say we wouldn't be a match, but here's what my book's about and here are my creds, and can you think of anyone where this would be up their alley? (But I also don't want to come across like I haven't been doing my basic homework, like scouring the internet for agents who *I* think would be up my alley.)
However, to answer your question, ask them about books they'd advise writers to read. Or books they think are really good. Ask them what they've read recently that they loved or hated.
Ask them what they wish all querying writers knew.
In other words, ask them about their tastes and preferences, not the tastes of other agents.
And certainly don't ask agents for info on who to send your book to. They probably don't know anywhere near as much about what other agents are looking for as you do. Plus, there's something a little offputting about a writer sitting down and saying "you aren't a match for me, but who else would be." Like asking a guy you don't want to date for info on the the other guys.