Maintenance is just like any other car, nothing different. The spark plugs are more of a bitch to get to, but nothing unique about service intervals or anything.
The 05-06's apparently eat wheel bearings like no one's business. My 06's were bad when I got the car at 38K miles. Not sure if the 07+'s are effected (07+ are the only Spec. B's with 6-speed transmissions).
The ride quality is fine. Not harsh by any means. The Spec.B will actually ride a little better, as the Bilsteins are quite a bit nicer shock. However the handling isn't much improved, still tons of body roll and pitch. I rode in a Spec. B with JDM STi Pink springs and Cobb sway bars - talk about smooth and flat. I'm going to switch to that suspension eventually.
I don't know why people complain about the interior quality. The plastics are fine. I wish they'd used padding on the door elbow rest things, but otherwise it's fine. If you want a nicer interior, okay that's fair, but the quality is fine for what it is.
The clutch takes getting used to. Frankly, I don't like it at all. It's vague and either the damn gears are spaced so widely or the flywheel is too heavy or the software doesn't let RPM's drop fast enough, because you have to wait forever for the damn revs to drop between shifts - esp 1 to 2. I'm not trying to rip gears here, I just don't spend much time with the clutch pedal in between shifts.
If I was any bigger, I wouldn't be comfortable in the car. I'm 6' 4" 250lb. I appreciate it's a smaller and lighter vehicle, but it is borderline for me.
The stock stereo speakers suck ass. The seat warmers take 10 minutes to get toasty (this is the only car I've had with them).
Frankly this is one of the few cars that you will find with decent power, manual transmission, AWD (or RWD), decent features (leather, heated seats, MP3 in 07+ models), decent MPG (lifetime average for me is 21 via fill-up, lots of short trips), and reasonable cost.
If you don't need the AWD, you might consider an Infiniti G35, but it will cost more for same year & mileage.
The Mazdaspeed6 is a great car, I test drove one before buying my 06. My main issue with it was that it was more expensive for the higher end model with leather/etc and it was a very limited run with unique drivetrain, so long-term reliability and parts is questionable. The handling was much better, the transmission much better, and power output a bit better. I think the seats were more comfortable too. That's one thing, I don't really like the seats in the LGT that much. They're okay, but I was spoiled my 06 GTO's perfect seats.