Some different thoughts if I may,
I got a TBI spacer and I'll be installing it tomorrow. Is it a gimmick? Probably. This is my DD and I'm combining it with 'cleaning and rebuilding my TBI' which I'm saying is necessary maintenance and I'm allowed to do anything to the truck I can justify as 'necessary' or upkeep.
Anyways, the real reason I'm getting one is because when I switched to an open reusable element with a flat bottom, (not the K&N one, save your money folks) I found that I could not remove the collar on top due to all the electronics as well as where the distributor is located and I figure 1" on top of the TBI will restrict airflow, 1" on the bottom will possible increase the effective size of the intake by a whole 2 cubic inches, or it will more likely have absolutely no impact. So a TBI spacer won't hurt in my application and will allow me to remove the collar and use a flat bottom air cleaner without having to perform any electronics relocation.
The other thing worth noting is in the sub-discussion about mpg, remember: your odometer is only as accurate as your speedo and while those miles are effective for purposes of service intervals if you're doing the trip odometer miles/full tank of fuel method you need to adjust your final figures for accumulated inaccuracies such as tires larger than 235/75r15 (stock size on my truck) which when I radar or GPS check my truck amounts to 10% which means that for every 100 miles my odometer says I've traveled I have actually gone 110 miles so if your odometer says you went 252 miles on 18 gallons of gas I first have to add 25.2 miles so I've actually gone 277.2 miles which means I would be getting 15.2mpg instead of 14mpg.
Sorry for all the extra words.