Best gas saver that I've found is the "Park" gear
Followed closely by "lighter right foot".
Lupinus, to answer your original question, throttle body spacers do work on some vehicles. How well they work depends on how poorly the original intake setup was designed and whether or not the vehicle has already been modified in other aspects. For your presumably stock vehicle they are usually a waste of time and money unless you have done some other mods to make it breath better. What mods it will take are determined by your particular vehicle.
The Tornados are a gimmick. They would be laughable if they weren't such an intentional snake-oil scam. The only two things they do effectively is restrict the flow of air into your engine and enhance the flow of dollars out of your wallet. Just say no.
Also be careful of the reusable filter setups. If you drive in dusty conditions I wouldn't use one. They flow better because they filter less. I have know several people who used them but switched back to paper filters the first time they took off the reusable and found the intake tract coated with dust. Others have used them without a problem. One very big problem is that they filters are shockingly easy to overoil. The excess oil sheds off into the airstream as tiny droplets which deposit onto the MAF sensor. Not a problem if you don't mind pulling the sensor for a cleaning every now and then. However, if you are the "don't bother" type when it comes to routine, regular preventive maintenance, I'd pass.
Probably the cheapest upgrade in terms of dollar for horsepower would be some type of cat-back exhaust system and a tune-in-a-box. Borla, Walker, DynoMax, Flowmasters, and others make direct fit replacement exhaust systems for many vehicles. One of those in conjunction with a SuperChips or some other type electronic tuner will net you an increase in power. Don't expect it to be a Honda-to-Hemi kind of change, though. Just something enough to notice, usually barely. That is, until you check your mileage.
Brad
yeah seems to be the general consensus is the things don't work lol. I'm thinking that the money would be better spent on a decent cat back exuast or an underpully system. No I'm not looking for nascar but you ever hit a big hill in 4th gear in an 87 s15 jimmy with that 2.8 baby in it? Not looking to build a race car but some more power would be nice lol.
I used to have a 91 S-10 with a 2.8... yep it sucked doing the big hill thing on highways. I do miss the 25-27 mpg I got with it.
My 98 Jimmy with a 4.3 will fly up any hill but it averages 14 mpg in town and 20 on the Hwy.