I believe the tire monitoring system was added in 2008. in retrospect when I bought our 2nd Kappa I would have bought an 09 mainly because most of the bugs had been worked out of the platform, and features that were optional on earlier years may have been standard by 09.
Also, I know you want a 2.4, however I think you should consider a turbo (and a manual). The reason being that turbo's w/manual transmissions will more than likely be more desirable and therefore easier to sell when it comes time to do so.
Also, SKY's were considered a more upscale version of the Solstice and cost more than a like optioned Solstice. That still true when it comes to used values. When it comes to options most dealers loaded them up to make as much profit as possible.
Here's a couple examples from Hemmings, though they tend to be on the higher side because they cater to collectors and auto enthusiasts.
2007, 2.4, manual, silver, cloth seats, 7,200 Miles, $18,500 negotiable
2009, 2.4, Manual, One year only blue, 20,609 miles, $14,995
I've been taking the summer off from posting high and low Skys, but I continue to stalk Craigslist on a daily basis. But once fall arrives I probably will start posting again. FWIW, I haven't been finding much of anything to post from Craigslist, but that might be due to Craigslist search parameters seem to change from time to time.