My daily driver is AWD:
Great for fast takeoffs on just about any surface. Totally awesome in the dirt and loose stuff with the adjustable center differential, I had an entire afternoon of fun a little while back on a friend's 650 acre ranch; the pastures had about 2" of greenery on the ground and it had just rained a little bit. It's also pretty much "idiot-proof" on the asphalt, but tends to push when driven hard, as AWD cars tend to do.
A well sorted 2wd will still get around a roadcourse faster, but if you are willing to give up a bit of max-effort cornering ability the additional straight-line traction AWD provides is wonderful. Lots of HP + AWD would be an evil combination for street tires as it will hook just about anywhere. Take it off the pavement and it really shines. High-HP Sy/Ty's, plus Nissan Skylines, Subaru STI's, Mitsu Evos, the Escort Cosworth, and a few others come to mind. There are many guys on the Subaru forum I watch pulling 1.5x 60' times on relatively narrow street tires (usually 225 wide) although that's rather hard on the drivetrain and clutch.
Plus, given enough power, you can do awesome AWD burnouts. The Top Secret-built Skyline (about 1200hp) does some WICKED 4-wheel burnouts.
I say go for it. I honestly thought about it on my car but given the size of the transfer case you're going have difficulties with headroom; if you want to keep the car low you're going to have to REALLY raise the floorpan for clearance.
Troy