I live in the Dallas area and I sprung a small leak in the copper piping leading into my evaporatoer in my upstairs AC system. I was given the option to replace with an equivalent part or with a "13 SEER" rated part for a couple hundred bucks more (total cost).
I realize that 13 SEER is not a rating for the parts in the house but that those parts need to be matched/rated appropriately.
After doing some reading on 13 SEER systems, I had some concerns that depending on implementation, installation, etc. having them put that equipment into my existing system, even if I replaced the necessary equipment outside, wouldn't give me even close to a 30% improvement in efficiency.