I own a 08 gts.
I don't look closely at my mileage so I couldn't tell you what my MPG is. I could only compare it to my last car which was a 1.7 l civic and I can tell you it's not much worse. When I was driving to work from Burnaby to Downtown and back every day I filled up about once a week or two.
Most people have bad things to say about cvt. It's actually not bad compared to a slushbox automatic. If you compare it with a dual clutch like a ralliart or a manual transmission, it kinda sucks. Initial acceleration from a dead stop is slow but once you're rolling it feels quick. CVTs are smooth as you don't get that shift feeling and my passengers always complement this. People complain about the sewing machine noise but I don't really notice it much. I also drive with loud music all the time
The paddle shifts are fun but they're a bit of a toy. I only use them when I'm bored or maybe shifting lanes.
If you go with the cvt don't even think about power mods. Any significant increase in power will put too much stress on the transmission. If you want power mods go manual or get another car. You can get your typical suspension mods. I've seen some body kits and there are some funky rear lights available.
Not too sure about the differences with 08-10. I think the newer engines have increased displacement and you can get a leather option. The current year ones have an all wheel drive option.
Reliability is ok. My problems included: bad radio reception (i got one warranty replacement, still kinda poopy but I replaced with aftermarket pioneer), my rotors warped after machining it once, minor rattle on passenger side door/frame.