The TF is a great car, much "prettier" than the MX-5 imo and if it's not a base spec one they're actually nice places to sit, especially with the half leather half alcantara interior. The 80th anniversary ones are the pick of the bunch, but are obviously more expensive and you can get a similarly specced one for much cheaper. It is fast enough and handles very well and is a hoot to drive. Sure the MX-5 is meant to be a better drive, but you're not going to be constantly throwing it into bends on the way to the shops. I managed to fit a £150 supermarket shop into a TF, so there is quite a bit of space, but the front boot is of limited use if there is a spare wheel in there rather than the rubber repair kit.
If you're buying it for your wife, she will love it, and will probably like the looks of it more than the MX-5. Unless she is a real racer, I doubt she'd drive it to its full potential anyway. That's if she ever gets to drive it, I'm sure you'll be fighting over the keys in no time.
As far as reliability goes, the later models (03/04+) are more reliable, with slight engine modifications to stop the dreaded HGF. Servicing and parts are still not a problem, JCB own the rover spare parts network, and former MGR dealerships will still service the cars. Anyway, the TF is recommencing production pretty soon, so there shouldn't be a shortage.
The 1.6 engine is a bit gutless as far as I can tell, the 1.8 135 variant is fast enough for some engaging drives around the local back roads, with the 160 probably being the pick of the bunch.