Of those investor-owned units, you may want to investigate if they have any financial or family connections to the condo management company.
If they have no connections, but their units have remained rented continually without significant turnover, you may have a hard time convincing them. But, if they have had problems with turnover or empty units, they probably would be very amenable to improving their return on investment.
To me, the whole townhouse condo-phenomenon is very curious. Coming from Philadelphia, where row homes in close proximity to one another were separately owned and maintained, it has always humored me why Massachusetts is so fond of the more expensive condo management arrangements. (The row homes were usually well taken care of, as long as the units were lived in by their owners and not involved with subsidized housing programs.)
Perhaps there are some folks out there that are familiar also with condo town houses that revert to individually owned and managed units? Would that be a consideration for your fellow condo owners, to eliminate the entire condo setup as well, eliminating the condo association and management?