Yes, I would say it's a noticable upgrade from the base system, but nothing huge. Really, it just gives you more speakers that are a little better quality. The sub isn't worth much and sounds really muddy. Heck, the whole system loses composure at moderate to high volume.
I kind of get the feeling you're looking at hatchbacks, but you never really said. The 4-door and 5-door subs are very different. For the 5-door, you can put a bigger sub in the spare tire center. One problem is how you're going to secure the tire if you block the path of the stock bolt. Also, if you do that and use a short bolt for the spare, you have to figure out how to secure the sub. I've done the measurements and you've got about 6" from the bottom of the rim to the under side of the floor. Even allowing room for the fiberglass and baffle, that should be enough room for an 8" (which would be MUCH better than the Bose 5" sub). That should also clear the center bolt (~8-1/4" from edge of bolt to edge of rim). I would try it myself, but I don't want my sound under the floor.
A jackbox/stealthbox is a better option, imo, and should be possible on the 2010's (I've done the measurements for that too). Either way, you'll be looking at a custom fiberglass enclosure, aftermarket amp, 4ga or 8ga wire from the battery, inline fuse, and a line out converter (on the front speakers). The stock amp is pretty worthless. It's 242 watts peak for the whole system and you'll want at least that just for the sub alone, lol.
Honestly, I wish I didn't have the Bose system at all. It's more of a hassle than anything. I really wanted a sunroof though and I don't trust a dealer to install one.