On the other hand, the SP1 quality cannot be beat. You could find a large pin upper to build it on if you want an A2, since they're still available if you look around, or just use the A1 upper from the SP1 (nothing wrong with an A1 arrangement in my opinion, and A1 sights are foolproof).
The SP1 doesn't have the fence or reinforcements of the later model, but they are the best quality lowers ever made, and all the other pins, etc is milspec size. I prefer them to the later Colt prebans with goofy fire control pin sizes.
Resale is a factor too, if you ever want to sell it. A Colt will always be more desirable than other brands (imo anyway), and therefore will bring you more money, all things equal. Also no question about whether it's really preban or not.