I expect that your 29 MPG for Interstate highway driving is just about right. I usually get 27, with country two lane driving which means I do some passing which increases thirst. I used to go to Houston and some other places with mine which were strictly Interstate trips. I could get 29 on those trips. Remember you don't have the inefficiencies of a torque converter swallowing more fuel.
My car, mechanically is as you describe yours, but cosmetically I need a windshield and a left front arm rest, and mine is embarassingly dirty right now.
Do you think that these cars are a little shy on bottom end and mid range torque? As far as how mine runs and drives, the lack of low end torque is the only complaint I have, the car seems geared just a little too tall. But I'm still very pleased with it.
I added the sportline sway bars to mine and it made a noticable difference. These are fabulous automobiles.
Glad you had a fun trip,