well, the first suggestions I can make in your quest are
1 - start benchmarking data on your 2 vehicles in question. I use apps on my smartphone for this. One is an OBD-II monitoring app called EngineLink, that gives me "real-time" feedback from the car's computer among other things; I use this to give me an idea as to how efficiently I'm driving based on instantaneous and average MPG, calculated from data the ECU sees. The other, Gas Manager, is a "check and balance" against the first as far as MPG; this one gives Long term as well as "by trip" or "fill" mileage. In my case, I started with EngineLink, and then stumbled onto Gas Manager. The numbers are in agreement with each other, or close enough. This gives me an idea as to how each mod/change affects (or doesn't) my Fuel economy, and thus my engine's efficiency.
2 - scroll down to the bottom of this page, and click on the link in the Gadgetmanland column "Was it successfully grooved?" list. It gives makes, models, years of grooved vehicles with their gains, or if there were any. keep in mind that just because your vehicles don't appear or see gains doesn't mean that they won't. you have to do some homework on your vehicles to see if they are similar enough to the ones on the list who have realized gains to give you an extra measure of confidence in applying the suggested modifications.
3 - try some things to see if you notice a difference, like the MPG Remedy, re-gapping your spark plugs, doing the PCV re-route and vacuum cap, applying RVS to your powertrain. That should give you some perspective and experience under your hood.
4 - Now is the time to do that tune up, fix those little issues that have been around for a while that you've just never gotten to.
I hope this doesn't discourage you. One thing that is clear is that this is a process, and you have to be prepared to undertake it to achieve nirvana.
