Besides you being able to show in breed shows down the road, if you add AMHA papers and cart training to him and "IF" you ever have to sell him you will get more than your money back.
Havent' read all the posts, but he could be hardshipped AMHA, also registered Pinto and I believe that if he has A papers, he can also still be registered R off the A paperwork!!
Bless you for rescuing him!! I bet he is in 7th heaven now! Minis are SUCH quick learners about stuff and just seem to be born to want to drive (most of them) so have fun with your little guy!!!!