I bought my '06, in April, after having it built in March. I wasn't sure if I should have waited till the '07 was released. In hindsight, I'm glad I did.
The differences between the '06 and '07's are minimal at best, and I agree with your assesment above.
I test drove an '07 in Sept. just to see what was changed, both asthetically, and design wise.
The motor, didn't inpress me. Looks great on paper with 242 HP, & Ft. Lbs. of Torque, but I can't notice 22 HP more. And with a price increase for this, I'm fine with the 2006, 3.5 liter motor with 220 HP/ 225 Torque.

The warranty, is because the motor is a new design. What GM dosen't spell out is that the 4 year/50k mile warranty hasn't changed. They just added an extra 50k miles to the power train only, so if there are problems with this new engine design, they'll cover it. That came from a phone convesation with HUMMER.
As for the look, Nothing was changed, other than some small motor components. Interior is identical.
The only litmus test to be used now is the deal on '06's vs. '07's. Sounds like not too many folks are interested in moving old stock. I guess they're holdbacks are okay to have vehicles sit on their lots for an extended period of time.
IMO, buy. Lease is great for low payments, but you'll have no equity in the future towards the purchase of another car.