Hey Seth,
I had the same concern about my wheels and how far inward they sit. I have some H&R spacers arriving shortly to fix this. There are a bunch of off-brand spacers out there, but the only ones I would be willing to install on my car are the H&R Trak Plus spacers. I got mine from SIX autoworks (
www.sixautoworks.com). They have the lowest prices I could find, and have been easy to work with. Tell them Greg from Hawaii sent you!
Oh yeah, depending on how thick the spacers are, the increased track would in fact cause the rear end to stay planted a little more, while effectively decreasing the rear spring rates to some degree.