Did I mention his new wife HATES the car and can't drive a stick?
The wife hating, can't drive manual may possible be used to your negotiating advantage (along with Pontiac an orphan brand), and how long he's been attempting to sell it.
Enthusiasts wise, the Kappa (Solstice & SKY) are considered "niche" vehicles mainly due it being a 2-seater; whereas Camaro,s, Mustang's (and Vette's) having a larger popularity base and longer historical history. The upside to owing a niche vehicles is that you're not blending in with everyone else. The downside is because the market is small not as many vendors are willing to introduce custom parts to help enthusiasts personalize their vehicles because not enough profit can be generated.
Performance wise, I'd suggest buying:
Solstice Performance Handbook 88958697
to give you an idea what the platform and mechanics are capable of, along with the Solstice book by Gary Witzenburg for the development history of the platform.
The Kappa is also referred to as a parts-bin vehicle even though the body & frame were unique; the engines, transmissions, differential, and miscellaneous
parts were parts-bin in order to hit a specific price-point. The upside is mechanically parts should be readily available, the downside is anything unique to the platform may get more difficult to locate in the years ahead. Pontiac Solstice - Wikicars
As with any niche vehicle while we may not be as popular (or have as many vendors) as the big-boys do, we tend to be a close-net community that welcome cruisers to hot-rodders, along with the casual enthusiasts. Some folks like that, others prefer the perks that comes from owning something more mainstream & popular.
Just know red automatic coupes are the fastest.