Update:
I did a couple of mods to my '93 last night.
First, I took off the OEM airbox setup and wrapped it with insulation tape. It took about 90' of the stuff, and I secured it with aluminum foil tape. This wasn't 100% necessary for most of the wrap, since it's pliable and semi-adhesive. I mostly just used the foil tape to secure joints in the wrap and to help cover the main box. With the thickness of the thermal tape, you can't just 'wrap' the box itself. you have to lay down strips, then cover the strips with foil tape. Anyway, it looks fine installed. It's shiny, even if it's not very sleek :-).
While I had the Airbox setup removed, I performed the Throttle Body coolant bypass mod that's been discussed here. I completely removed the rubber/metal/rubber hose that runs across the top of the radiator and to the Throttle Body. Then removed the small rubber hose that goes from the Throttle Body to the intake. I then used a 3' section of 3/8" hose to bridge the gap between the radiator and the intake, bypassing the throttle body. To clean things up a bit, I used a 1' section of 3/8" hose to connect the inlet and outlet coolant lines on the TB. After that, I re-installed the wrapped airbox system with a K&N filter.
I don't have a great basis for comparison, because it was 85 degrees outside when i drove home from work yesterday, and it was 54 degrees this morning (currently 55). The cold front we had last night cooled everything off and helped my truck breathe better, so I'm not sure how much effect these mods had. I can tell you that there was definitely a noticeable difference, but how much was mod, and how much was cold front... i dunno.
My total cost for this project was as follows:
K&N filter: $45 - AutoZone
90' of insulation tape plus foild tape: ~$22 - Home Depot
4' of 3/8" hose: ~$4 - AutoZone
So for $70 or so and about 2 hours of work (mostly wrapping and taping) I am now burning much colder air, and more of it. This in combo with my 33" tires should give me decent mileage. Once the outside air heats back up to normal, I'll recalculate my MPG and post it in this thread. Anybody with questions, please feel free to email or post. I'll answer if I can. :-)
-Josh