This $200 rebate, to qualify, do they say who you have to get the next
one through? I feel an inflated installation charge/unit price coming.
I imagine they will restrict you to buying a gas unit over electric so
what other rules are in there?

If you can go to Sears/Lowes/HD and get a new one installed for $400 or
less, and still get the rebate, then that might not be a bad deal.

Mines 26 years old and on its 3rd set of elements(electric). I drain it
every two years and check the elements. Have you been draining it to
remove any sediment build-up?