I have two that are relevant to this conversation.
a 2004 Denali XL
and a 1985 Suburban 3/4 ton diesel
I'm keeping the Suburban, parting out the Denali (despite that I just drove it 2500 miles to California and back). I've also owned a 1993 Suburban (350). I paid almost exactly the same dollars (including costs of necessary repairs) for both of them (just under 3k). The Denali had 184k, the Suburban (a guess) about the same miles.
Impressions:
The Denali gets 13 mpg in Seattle driving and got a best of 18.6 on the highway. It's typical highway economy is 15-16. We have 3 dogs, a English Mastiff and two Bloodhounds. We had two cages, our gear for a week, and my wife and I comfortably in the 'burb along 2 other (flat) dog cages for a friend who was in an HHR. It drives very nice and is quite comfortable. I have an H3 Hummer with a 5.3 and I am totally missing the power of the 6.0.
If you're towing a trailer, this thing is equipped for it - it has a trans temp gauge, all the wiring necessary for a brake controller, and a button that firms up the shift points so that you don't burn it out towing a trailer. It comes standard with 4 seat heaters and individual control for HVAC (front, back, side to side) and a DVD player for the kids (that can be listened to solely by headphones thus allowing the parents to rock while the kid listens to Barney - or whoever this year's annoying-kids-show-is)
It IS AWD - which means that you do not have 4 low.
Which leads me to impressions.
It has a lot of electronics that fail. Mind you, the safety stuff, the engine stuff, the trans stuff are rock solid reliable but all the other 'features' fail pretty often. The rear wiper doesn't work, fogs don't work, lights are abysmal, and countless little things that just don't work. This one has a salvage title - and it's obvious it was wrecked at some point in its life.
Mechanicals - GOV locks suck. There, I said it, it is failing in mine, it's failing in a friend of mine's Suburban - it is not a feature but an issue. The air ride system says there's a problem, but it actually works - so I ignore the warning light. That said, it's not a cheap fix if it fails and many (like Land Rover owners before them) simply eliminate it. Idler arms are an issue (and they come in 2 parts, so be wary of that) - and they are also an issue in the prior generation.
That said, I'll end on a positive - the power, the economy, towing ability, the ride comfort are really, really nice and demonstrate why no one else even comes close to selling as many of the Suburban-based trucks.
which informs why I'm parting it out (the motor is going in my 76 Corvette and the trans will eventually end up in my H3). It's job is to be my suburban until my real suburban is done.
I have a 1985 Suburban, diesel, 4x4, turbo. It doesn't ride as well, is beyond slow (glacial) but it is dead nuts reliable and does everything I NEED the suburban to do. Tow my stuff to the trail head, go camping for a week, haul my dogs in adequate comfort. It doesn't have a DVD player, heated seats, power mirrors, or the ability to run 80 mph and get 18 mpg. It gets 15-17 mpg and will get 22-25 mpg when I'm done (putting a 5 speed in it). I'm lifting it so that I can run 35s and will use softride springs. It will never, ever ride as well as the Denali and its lifted height will require stairs so my dogs can get in. It is solid axle, a 12 bolt front/14 bolt semi-float in the back (which aren't optimal, but do save on weight).
So why would I do this? give up comfort, negligible fuel economy, and lots of creature comforts for the same money? because it's my RV. When I'm driving it I'm not in a hurry to get anywhere quickly - I'm on vacation. My DD is a H3 Hummer and that varies with my mood - next will probably be a new Corvette or perhaps a new pickup... but their job is to do what I need them to do - reliably get me to work. You mentioned getting a cheap commuter car to go with your Suburban - My 2 cents is why not buy a cheap Suburban, build it to your spec, and get an expensive commuter?
No matter what, have fun, post pictures of your build and don't let the turkeys keep you from having fun with your rig.