It's great to see someone happy with a particular mod. Wheel skirts, after extensive A-B-A testing, have been shown to work with some models of vehicle, not with others, as have some other modifications.
We are not here to tear down others' work, although it is just fine to be skeptical and ask for more detailed information. The original poster has thoughtfully provided more info, which is always a good thing.
Positive and negative inputs are just fine, but the way in which we go about it needs to be tempered. Constructive criticism can be harsh, but does not need to be mean or needlessly sarcastic.
We're not trying to discourage free thinking, or questioning effectiveness of modifications, but cruelty and meanness will not be tolerated. Just because there is free speech in the US doesn't mean there aren't consequences. Also, this board has rules, and courtesy is certainly one of them. Violations of these rules will be and are enforced.
Looking to trade for an early 1988 Honda CRX HF (Pillar mounted seat belts)
With regard to notion that cars with shorter rear bumper extensions benefit less, I've always had it in my head that rear skirts could still be a benefit if they are open to the rear similar to what you might see on a touring car instead of closed off. I.e., give trapped air somewhere to go.