Gen 2s and Gen 3s before the SF model are bricks in comparison to Gen 3 SF and Gen 4 models, which may effect your ability to sell. Of course, some like the older, wider models and Gen 2 Glocks of all varieties were pretty nice in terms of features. Performance-wise, any Glock 20 will be great.
If you plan to keep and shoot it, you might check out a Gen 3 SF and and Gen 4 before buying the Gen 2 just to compare grips and comfort. Despite liking large and full grips, I personally do not like the grip size of G21s and G20s before the SF and Gen 4 variants, which I always thought felt like holding on to a 2x4, though YMMV. Gen 4s have terrific reliability (as do all G20s), better chamber support, and very likely no need to replace springs if shooting hot loads as so many became accustomed to doing with Gen 3 models.
I love 10mm Glocks, but for $400, I'd still be on the fence simply for the grip. If you like the grip, it's a definite go IMO.