Until they do a new 1M, I think you're right. Then the market will settle back down we'll have some sense in 1M prices.
Think about it: A new 1M isn't going to be massively different from what the old one was. They'll use the new M4 chassis (which is better than the old M3 chassis), they'll use a S6TT engine (which will have more power than the old S6TT engine), and they'll still offer a manual 'box (as well as the amazingly impressive current 8spd ZF auto). It will also look better, given the 2 series looks better than the old 1 series coupe.
Unless they make a dramatic change on that, I cannot see original 1M prices holding anywhere near firm.
And saying all that, it's still an amazing car and I would love to have 1M on my driveway!