There are a lot of differences between the Solstice and Fiero, not the least of which was the rear engine configuration of the Fiero, which made it a real oddball. From what I understand, based on a conversation with an engineer familiar with the car, the biggest issue with the Solstice is fit-and-finish. I've seen several of them in my position, including a test vehicle or two, and have noticed some problems in this area. If you take a close look at the car, you can see that the way the body structure is designed is a little unconventional for GM. I don't mean that in a bad way, just that the car seems to be proving a challenge in terms of lining things up straight. I haven't heard anything about unusual mechanical problems. Besides, that Ecotech engine is well proven. The car also has a near 50/50 weight distribution, which is great for handling.
If it were me, I'd give them a year to sort out the fit-and-finish. If that doesn't bother you, go right ahead.
In terms of production numbers, they're currently building 20 - 25k cars per year. Starting in January, the plant that builds the car is adding a third shift that will boost the output to 30 - 35k cars per year. There is apparently quite a waiting list for the car right now.