After my crash with the trainer tire (less than 1 mile from home, BTW), I did go the route of having a rear wheel specifically for the trainer - changing wheels is a lot easier and quicker than changing tires, especially when you want to get out on the road. It's also harder to misplace a wheel.

Of course you should be the judge when it comes to using the trainer tire on the road. "Squared-off" sounds like an angle to me, however. So I would tend to err on the side of caution.

I would also guess that tire wear on the road is a bit more even than on the trainer, since in general (I'd hope) you're not doing much steering on the trainer - just the regular contact area with the trainer on the rear tire. With my trainer (Minoura Hypermag Alu), unless you have the flywheel set just right, there will be sizeable rubber flakes coming off the rear tire. Just another vacuuming opportunity, I guess.