I seem to be bottoming out my back suspension a little too often for my liking when I've got one or friends in the back seat of my 4 door Sidekick. Would switching to XL7 springs be too rough of a ride, and will they lift the back end up? Right now it sits level and I want it to stay that way.

Cmon now people, I'm sure someone's done this.

i have xl7 rear coils in my 03 2dr tracker with a 1.75inch heep spacer.  i heard the springs give 3inches of lift but did not experience that.  they are stiffer without question, with a load they also ride fairly nice, empty, i feel the harshness of the stiffer spring but that's to be expected.  you'll have to try them out to see what result you get.  i'd say if you can find some cheap used coils go for it!  they are noticeably thicker in diameter than mine were.

Hmm, sounds a little overkill. I think GV springs might be a better option...what do you think?

that's my experience with them, don't forget, i have a 2dr softtop so it's quite a bit lighter than yours.  i wouldn't expect that gv springs added to a 4dr tracker would make any difference, the 4drs already have springs for the weight of the vehicle they're in, which is not much different than a gv.  without the big spacer they didn't sit quite high enough and when loaded up still had noticeable sag, but rode very nicely.  if you figure your rig sits level right now, well, when you've got people and/or gear it's not level anymore, i wanted to sit level loaded up, so it sits higher in the back when empty which i am good with.  go for it - with the stock springs i would experience bad things at speed on the highway when fully loaded, ie bottoming and rubbing at speed, never happened on the highway again since installing the xl7 coils.