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?