Update - I have been commuting on my steel racer and on my Dahon Boardwalk, on alternating days.
I tuned the Dahon, installed a proper saddle and clipless pedals, and pumped the tires up hard.
So far, the most obvious difference is the upright position and squishy handlepost of the Dahon. Lots of wind resistance, and when accelerating the flex in the handlepost is obvious. I think I can address that with a shorter handlepost.
The next difference is not enough stretch-out room on the Dahon. I think I will stick some bullhorns in the shorter handlepost. It would be nice to find a seatpost with some offset.
The final difference is not a big enough gear in the Dahon. Where I'm 53x12 on the racer, in the folder I'm . . . nowhere. Mulling over doing a front derailleur mod to the Dahon. This really is a problem.
The small wheels are not feeling as odd as I thought they would. I am enjoying the ride, actually.
I'll be very interested to hear (and
*cough cough* see) how your folder evolves. As you're discovering, there are a lot of tweaks you can do to make your folder fit you (almost) as well as your road bike.
Again, don't forget the pictures.