Powertrain warranties for original Mirage owners are great (10-year/100,000 miles), but someone (like Dirk) who buys a used Mirage isn't going to have that security. If I owned a CVT vehicle, I would change my fluid/filter every 30,000-40,000 miles. Maintenance is always cheaper than repairs.
Personally, a good warranty (or extended warranty) wouldn't make me feel any better. If my CVT went out at 105,000 miles (made it past warranty), I would be even more ticked off. If a well-maintained transmission can't go 250,000-300,000 miles without issue, it's a step backwards.