The fuel economy on my FZ09 wasn't very great, but otherwise it was a very fun bike. The suspension is very on the soft side, so a lot of guys end up getting aftermarket suspension or rigging up shocks from other bikes (I think some Kawi ZX shocks worked okay for them for cheap). It's comfortable on the street though, so only starts being an issue if you're being very aggressive on the street or are going on the track. The seat, tank shape, and front forks are better on the MT09 (vs the FZ09). I would highly recommend it to anyone looking for a second bike (after a starter).
The MT10 is more powerful and heavier, and is similar to comparing an R1 to an R6 (the R6 being more like the MT09). I love the sound, the looks are subjective (I like them), but it's hard to say whether the value is there compared to the MT09. I'd say it compares favourably to the competition (SuperDuke R, S1000R, Tuono, etc.) and liked it more than anything else in the class (I haven't tried the Tuono, mind you). Whether you need this much power on the street is questionable, but I also ride a CBR1000RR, so I would obviously say "Yes" to that. The suspension felt fine to me on the street and with an exhaust it would be perfect. The ergos felt nice to me, where the MT09 is a bit small for me (I'm 6'3 230lbs though).