I can concur with the "Not Stupid" camp. I have been running the Grand Bois Hetre on my Trek Crockett disc and can't say enough good things about them. The ride of the bike was transformed. With the right tires this is much more than an incremental improvement. Mine are set up Tubeless on Velocity Blunt SL Rims. There is zero penalty riding them on smooth roads and huge gains in rolling resistance and comfort as the roads turns rough or too dirt. I've never had an easier time riding on freshly graded or loose gravel. The problem with large 700c tires on the road is that they start to feel like wagon wheels. The smaller 650b keeps the overall diameter in check and reduces the gyroscopic affect of all that weight spinning at the edge of the wheel.

The Hetres wouldn't be my first choice for trails but that is what the newly introduced 650b Soma Cazadero, Surly knard, and Bruce Gorden Rock and Road will be for when I get my hands on them. These are all 40+mm light knobby tires. If your bike can fit 2" tires there are options from Vee Rubber, Schwalbe, Maxis, etc. I would go for the biggest tires on the trail to avoid pedal strikes as mentioned above. Obviously a drop bar cross bike is never going to be a complete replacement for suspension MTB on trails - but I think you knew that.