Should I remove my zone-cooling??

Our single-station HVAC system has been tricked into being zoned (dampeners/bypass duct). I like it. I get 3 thermostats to control different parts of the house. The HVAC doesn't like it. Lots of static pressure and sweating on the unit has rusted our furnace and left mildew/growth in plenums.

I have tech who wants to make it 1-zone and remove the dampeners and bypass duct. I have another tech who will replace the plenums, redo ducting and dampeners, and squeeze more juice out of the system. A variable stage inverter/condenser is too much and I am not dropping 30k. Home is 1 story and I plan to move in <5 years - resale value is important and I think a 1-zone system might turn people off. What do you all think?