There is an engine modification that is a win-win-win proposition in almost every possibly way except the ease of doing it, . . . and like nearly any other engine work, it is a lot easier to do on a 2-stroke. Establishing a good tight squish-height gives an engine better swirl, slightly more compression with probably less tendency to detonation, more torque, AND better fuel efficiency, ta-dah!, and a great feeling of pride on the part of the fellow who does it, not least because he feels himself part of the somewhat limited in-crowd who knows about the technique.
I'm guessing nearly everybody here has at least heard about squish (Brit. "quench"). Any amateur mechanic rightly should know, since the technique dates back nearly a hundred years to Sir Harry Ricardo (who also pioneered water injection). Setting the squish on a car engine has to wait for when you're doing an engine overhaul, since it involves machining the deck surface of the block. But on an old 2-stroke bike it's not a huge deal to pull the jugs and deck them, and with certain engines you can set squish by shaving the head(s), and leave the cylinder(s) alone!
You can also make a 2-stroke (or whatever) a bit more fuel-efficient with piston coatings and with exhaust system thermal wraps, and a few other tricks.
This is mere supposition, but I believe that after I overhaul and upgrade (for fuel efficiency and longevity) my politically-incorrect 35-year-old RD400 2-stroke, its total environmental impact over, say 100,000 miles (yes, it's do-able), including fuel consumption and emissions, will be less, far less, than the total environmental effect of a brand new Prius being manufactured, shipped across an ocean, and driven 100,000 miles here.
I comfort myself with this thinking every time I overhaul (and improve for fuel efficiency) any old car or truck (admittedly I choose them for their fuel efficiency potential, which wasn't the case with the RD400).
(Uh . . . I have to admit that MY RD400 would do better in this comparison with a Prius than would anyone else's RD400 . . . because I'm getting too old to ride an RD like it's supposed to be ridden).