I think Brompton will last longer and will have better resale value. So I think if you are going to use it regularly over a long period, it would be good to save up for a Brommie.
Yeah, I think you guys are right. For me, it's close to a wash; leaning in favor of Brompton in the long run and Dahon in the shorter run. I'll probably end up getting a Brompton eventually and keep one, or both, Dahons on the side as a backup/secondary bike.
Other than the size of the 20-inch Dahon, the lack of any rolling system other than the front-wheel-roll-with-seatpost-up trick is kinda annoying... Like other folders, Dahons don't have much functionality in a folded or partially-folded state unlike Bromptons.