I'm a huge sporty Toyota fan... I love my IS300, and the MR-Spyder has always intrigued me. It's very light (2200 lbs), so I'm betting it'll be much more tossable than the already nimble Boxster. The MR isn't particularly fast, as it only has 138 hp, and the mileage is similar to that of the Boxster. Practicality goes to the Boxster... the storage capacity in the Toyota is a joke. You're probably right about ease of ownership, especially with a Toyota built during one of their strong periods.
Unfortunately I haven't driven one (they are hard to come by), so I can't give any back-to-back comparisons. The Boxster does sound better though... far better.
If you do get the MR, don't get the crappy SMT automated manual transmission. I've heard nothing but complaints.
They're both quirky and somewhat unique cars that'll be more than enough to put a stupid grin on your face. The Boxster will be more practical everyday, but the Toyota will be more Toyota everyday...
