i guess it depends on age of unit. having been in HVAC field you can tell the difference between a unit 10 yrs old and something 1-2 yrs old in efficiency and cost to run.
It will cost more to get a new one installed for sure, but depending on what the issue you have going one is the repair may be half the cost of a new one.
Guess you have to decide to spend more now and get the benefit of better technology or spend the same over time with lower efficiency = higher operational cost.
Carl, Raleigh NC
2-24-16 got a 2005 Classic 31D
Timeshare owner/user since '99
TUG2.net check it out for good rental deals
2003 F-250 SD, CC, 7.3L PowerStroke
, Piedmont Unit #161, Region #3