Itunes runs like crap on my 8-year-old laptop, but I don't really expect it to be that fast. Anyway, I need it for my iPhone.
I think feature crawl is the biggest thing for me. It started out as a really good manager for music and iPods. Apple added TV shows, Movies, applications, ringtones, contact and calendar syncing, photos, etc. Now instead of being a slick interface for music, it's a bloated, jack of all trades master of none.
I think they should rewrite iSync to be just like iTunes (look and feel). List all devices so you can manage them without having them connected. Add in applications and the app store and leave it at that. Or make something like doubleTwist into the new iSync. Call it "Mobile Device Manager" or something (MDM sounds Microsoft-ish, totally accurate, but uninspired).
Pull out everything but music, movies and tv shows from iTunes and rename it iMedia (or something like that).
How would this improve anything? You are adding more overhead, more confusion, and more room for error by dividing the features into two separate programs. What are you gaining? You said you used to like the interface for managing music. What has changed for the worse in the interface for managing music? Very little.
Also, the renaming thing seems to come up alot. What's up with that? It's a huge brand at this point. Burger King isn't going to rename themselves "Assorted Fast Food King".