I have a 2006 Mazda 5. Aside from the fact that I had to deal with 3 major TSBs for a first year model, I have had no problems with the car. There was a rear wheel tire wear issue with the first two model years, but it hasn't been a show stopper for me. The 06 honda civic had the very same issue, but I think Honda handled it better than Mazda, because Mazda didn't handle it at all. I have 81000, and the car still pulls like it came from the showroom. I'm taking it on a 1500 mile road trip next month in the desert, and I have no concerns at all.
I saw the latest model 5 in the showroom yesterday, and it's better than the outgoing 5 in almost every way, except for the styling. The sliding doors are even easier to open, and they have a silkier feel. The quality of the interior is WAY better. They made significant improvements on interior - materials quality and more importantly, touch points. The sterring wheel and rotation of the climate controls feels expensive. The seats also have better support. They improved the front seats, so that they more comfortable on long trips. They have better arm rests on the first two rows.
I personally like the 2.3L better, but the 2.5L is Just enough to make the car more driveable without having to resort to the tiptronic to gain power when the car is loaded. They also resolve the rear tire wear issues.
Would I buy the new one? Yes. Why? Because all in all, the new model is mechanically and practically better in almost every way. The platform is the same and demensions and size are still the same, which is a good thing. It's also become a better car for long trips.