The newer Pioneer units do indeed pull their maps from internal (or SD) memory now, leaving the disc drive free. I have absolutely been looking at the AVIC units, but the prices are a little offputting, when I dont know what I'm going to need to spend to get my speakers set up how I want them.
The 500bt isnt actually an in dash unit if I recall. It's just a large flat item that you can sit on top of your dash. That's not appealing to me. Once I'm all done with everything, I'd like it all to look pretty clean.
I have been eyeballing the 700bt, 900bt and 90bt, which look like they may be around the lines of what I'm after. Of course, they cost nearly as much everywhere as I can find the newest version for. I've found the x910 down to $7xx, which makes $6xx for the older units a little harder to swallow.
I'm fine without a disk changer. I mostly do mp3 and radio. I have a large collection of CDs, but after I rip them to my computer they tend to just get boxed up and stored.