From a reliability standpoint, the best modification is probably to leave it stock. Any deviation from what the factory designed is potential for less reliability. However, that isn't much fun. ....................
Nail on head. This is one of the reasons that buyers shy away from modified vehicles. Working on stuff because a "mod" screwed something up and/or reduced it's life span ain't fun either; particularly when you already have some miles on it and normal maintenance becomes necessary. Someone replaced the radio in my last car. When the piece of crap replacement had to be replaced, I found that the idgit had cut out the factory harness to match the radio, instead of cutting the radio to match the factory harness. This created a lot more time and work for the process of replacing it. For my prior car, well into it's life, there were some things that I modified. They were modified to help mitigate design flaws. Gasket maker on top of the strut towers. (water & road salt would sit between the strut mount and body) Ran a cold thermostat. (early aluminum head, iron block design - different expansion rates created premature failures of their H-Gaskets) Honed-out the caliper slide mount bores. (calipers slide mounts would routinely lock-up - slowly warping rotor sets)
As far as this vehicle, so far, watch your temps, watch your coolant levels and just perform the regular maintenance.
The HVAC blend door system is truly a failure point. The system is
constantly making minor adjustments to the blend doors when you have it set on something other than "Hi" or "Lo".
Things that stress the blend door servos are:
* Frigid temperatures
* Adjusting while blower on full
* Adjusting while windows are open at highway speeds (due to high negative cabin pressure)
You can't avoid frigid temperatures, but just keeping the blower off or on a lower speed *before* shutting down the engine will help prevent "premature" failure.