A SEER 13-14 system can run $5-6K, while a SEER 22 system can cost upwards of $15K (as a guesstimate). In theory, a SEER 22 system can pay for itself over the long-term due to reduced electric/gas expenses. The issue is that higher SEER systems, above 16 I believe, rely on variable speed motors. My understanding is that they are inherently less reliable.

A SEER 13-16 system might last 15-20 years (if you're lucky), while a SEER 22 system could break down much earlier at about the 10 year mark. You can sometimes replace specific parts, but depending on what breaks, it may not be cost effective.

In short, the only way we're moving to more efficient AC systems is if costs come down significantly, we see some major innovation in the field, or the government provides significant financial incentives.

As an aside, I also think we could achieve energy efficiencies by increasing the insulation in houses. It's unbelievable how much hot/cool air is lost through windows, doors, crawl spaces, and attics.