We tow a '10 172T. Same as the 176T, but no slide out. You are spot on regarding more space. Maybe not for the obvious reason, however. A lot of the time, we use the popout bed space for storage - bags, towels, etc - and the dog sleeps up there. My wife and I will then sleep on the dinette. Our two girls are in their bunks and are in heaven. I'd like the slide out option if we were to do it again. It's a bit cramped without it. Tough with four people in the camper when you're washing dishes and someone's heading to the bathroom, etc.
The biggest drawback on the popout IMO is setup (which really isn't that hard) and temperature control. We live in MN like to camp early and late in the season - "bug-free" camping. The popout tent does not hold heat well so the heater is on and off all night long like crazy. That's part of the reason the dog sleeps up there - the fan on the heater scares him!
If we had to do it again, I'd look long and hard at a 176T, a 179 or a 182G. Not sure the 179 would pass muster without the bunks though. I like the idea of the garage. Move inside work to the outside.
Another thing to consider is the R-Dome. It's a great addition that adds a lot of private outdoor space for things. Really helps keep the inside from being cluttered after you get unpacked and settled in. Feel free to pm me if you have more specifics.
Good luck and welcome!