Actually I think you are very small-minded, typically us'an in this respect, to consider the USA " the real world" as regards private flying. You really believe European countries are the exception?
I said nothing of the sort, nor did I say that the USA is the "real world." Just part of it.
Europeans tend to believe, particularly insofar as this forum goes, that the edges of the known world end at the edges of the European continent. It just ain't so.
Then again, European aviation is a drop in the bucket compared to the amount of flying that goes on the US.
Europeans don't seem to complain about it much when they come to the US for training, rental, and "time building." Just when they get home; that's when the arrogance returns.
Before you accuse me of being too provincial and isolated in the USA, let's not forget I live in a lot more of the world than you do, and operate over a considerably wider geographical area, among a lot more cultures, and I'd wager to say I've likely had residence in far more countries and on more continents than you. Perhaps that's isolated in your opinion, but I'd beg to differ.
Nowhere in the world is an aviation system as large, pervasive, complex, or as developed as the US; particularly so with regard to general aviation. Given that it's the largest and most complex and most developed aviation community in the world you could correctly say that it's the real world, but some of us live in the larger world, and you can rest assured that there's more flying around the globe than what is to be found in the confines of Europe.
If you truly want efficiency, get a Long EZ. There are more efficient aircraft than the 172, to be sure, and there are less expensive aircraft to operate. A hang glider is less expensive. You'll find fewer airplanes out there built in the numbers of the 172, with the parts availability, with the universal recognition, the ease of insurability, the benign flying qualities, the simplicity, the ease of maintenance, and cost of the 172.
Are we going to see the 152 come back into production? No, not really. It's a shame, but time moves on. I'd love to see the Super Cub come back into production, because although improvements continue on this venerable design (the Carbon Cub, the Husky, etc), it still continues to hold a high value among those who put a premium on the capabilities the cub offers; it's still a much sought-after airplane.
The cub isn't going to see production again, not like it once did, and the 152 isn't either. Experimental aviation has long been, in my opinion, the salvation of the future of general aviation; it's been the developmental world for much of what we're seeing emerging today. I'm a big proponent of home building; I have aircraft under construction personally, and I'm a former Experimental Aircraft Association flight advisor and technical advisor. Each of my children got their first airplane ride as "Young Eagles" under the EAA program. I'm all for homebuilding and experimental aviation.
It's not realistic for many, however, and the fact is that far more people who begin building an airplane fail to complete their project, than actually finish them. Experimental airplanes have become more expensive than used production airplanes. Even used experimental airplanes such as an RV-6 are expensive propositions, particularly those equipped with anything other than bare-bones day-VFR instrumentation.
Avgas in the US isn't cheap. It's a big part of the reason that the EAA pushed for, and received ongoing Supplemental Type Certificates for a number of different light general aviation airplane applications for auto fuel, or MOGAS. I'm not a proponent of auto fuel in airplanes, but I've certainly flown airplanes using autofuel.
A couple of years ago I audited the fuel burns for identical type aircraft being used in a particular operation involving piston airplanes. I found that my own fule burns were 75% of what most everyone else was doing, and upon closer examination, easily determined that the reason was poor leaning practices. The ability to operate economically is partially due to the pilot and his or her willingness to use good practices, rather than mindless blanket approach many pilots use. Given the frequent admissions we see here that instruction isn't being provided in basic aircraft operating practices (including use of the mixture), it's little wonder that some might see a very economical airplane as a gas-guzzling monster.
In the case of the 172, it's just not so.