Like a lot of the high efficiency stuff ...
The money saved for the sake of energy efficiency will be more than lost once a repair is needed. Not only the repair, but I am doubtful that some of this "high efficiency" equipment will last as long as the one that was replaced.
The question that I am asked quite frequently is, "Why is it that my new high efficiency heat pump cost more to operate than my 15 year old heat pump?" I don't have an answer for them.
I am starting to believe that all this SEER & HSPF is a bunch of hot air. If the long term or lifetime cost of the system is figured in, I am sure that the old 10 SEER system was a better deal.
Just my $.02.
But as far as an ECM motor replacement goes, you could put in a PSC replacement.