I own a 2000 Millenia, and have had it for nearly three years. It now has over 109K miles on it, and other than a "check engine" light issue, I've had no trouble at all with it. After investigating the cause of the light. I've found thus:

Trouble code says "P400"--EGR flow restriction. After conversing with a local mechanic employed by a local Mazda dealer, he advises that the EGR system takes the exhaust and re-routes it back through the intake, thus creating a high carbon density in the intake manifold. This density, among other things, blocks a small "pin hole" in the manifold itself, and the code pops up, and the light comes on.

I've had the manifold cleaned by this dealer after trying some heavy-duty intake cleaners (Run Rite), which improved performance immensely, and having changed the EGR valve, but didn't cure the trouble code. Approximately 45K miles later (today), I'm having the entire intake removed and cleaned out (not by the dealer this time, but by another certified mechanical shop) and re-set (approximately $300 which, in my opinion, is a small cost that reaps long-term rewards). This should solve the problem for a long time to come. I do a lot of driving in my work, and I love the car--the interior, comfort level, amenities, etc., and I'm 6'2" tall, and appreciate the extra space afforded. I typically own a car well into the 250K mile or more range, and appreciate the value of consistent maintenance--the life of any car. The car is a beauty--black with grey rocker panels, tinted windows, sunroof... when it's clean (most of the time!), it's a real eye-catcher!