The truth is, Dennis made Minimig mainly to show himself that he can do it. He didn't think at that time if it's going to cost more than an A500 or if it's going to make any economical sense. It was an opportunity for him to achieve something that nobody ever did. And he did it. Thoughts like, what next, what to do with it now, came later. He decided to open source it to let the community get the most of it. Being open source, it can be enhanced by others or simply produced. It can fork in many directions. It was at no point created to let anybody get a cheaper A500, it was a hobby project all the way. And it's great that even when it costs more than an A500, there are quite a lot of reasons (already pointed out in this thread) to want it.
Minimig is just cool!
Thanks Dennis!