Your TL would be worth quite a bit more than the G8 in 3 years. There is no way the G8 would be a collector's item. Things only become collector's items if it is well loved. This car has not sold many even though has decent performance. Some things die because it does not sell like Pontiac products and for good reason.
No one goes "Oooh, there goes that Pontiac G8!" It'd be more like "Oh... you have a Pontiac G8?" and thinking to themselves, "why?"