I guess I'll throw in my 2 cents here. With not a lot of work, you can make your LS plenty of fun. My first delta car was an '09 1LT 2.2 5spd. While it was fun to check it's limits in stock form, said limits weren't very far. After a while, I managed to find some SS Suspension and wheels(with fatter summer tires) to swap on, and I ended up doing a TWM shifter and SS rear axle(disc) swap down the road, along with a ZZP downpipe and 2.4L catback, to open things up a touch and make a little more noise. This thing was a blast to drive. No, it still wasn't very fast, but with the 5spd, it still had enough torque to set you in your seat in 2nd. I was more than able to keep up with the SS guys both on twisty roads and in Autocross(sometimes I was quicker). All in all, those mods probably only cost me about $2k(installed it all myself, so that saved a bit).

Now, if you are set on being significantly faster, than you are going to want to look into a SS. I traded my LT for my Cobalt SS Sedan, and it is night and day. As far as handling goes, the SS doesn't handle much better than my LT did, and that could be attributed to the 300+lbs weight difference. Now, I don't even have a real tune on my car(STG1), and it hauls. I keep up with trifecta HHR's. As far as the SS compared to ST's and Speed3's, there is no comparison. They handle about the same, maybe a little favorable to the ST and Speed on a tight course, but straight line, neither will keep up with the SS. Fully bolted and tuned ST's are barely breaking 300whp, whereas it's not uncommon for the SS to hit that on a tune alone. A friend hit 304whp with a catless downpipe, a 23psi tune, and a slipping clutch. On a standard track, there aren't many sport compacts that will beat a SS stock for stock, or even mod for mod.

As far as reliability is concerned, in those ~80k miles I had my LT(got it with 32k), the only things I had fail, was a headlight bulb, tail light bulb, and the reverse light switch. I've also had very little trouble with my SS in the ~10k I've had it.

The downside to trading up, is our cars don't hold much value. My '09 LT with 108k miles, I was offered $3k by the dealer. I had to fight to get $4k. Even 3rd party, I would have had trouble getting $7k. The least I've seen a SS in good shape with less than 100k miles was about$10-11k. So, you can pay that, and have an already competent car, that will be a blast to drive. Or you can spend a little money, and make your current car a lot more fun to drive.