Mr Guppy,
You are somewhat bewildering me by terming the C152 and C172 "very economical to operate". Isn't the economy of light aviation changing rapidly? The Cessna's are probably less expensive to operate than a Stearman or Staggerwing, but in today's G/A market they are on the expensive side.
The total cost of operating a plane is of course composed of fuel burn plus maintenance plus a few minor others, and all factors vary between places. For a 4-seater, the C172 has its merits and its place in the market, though the twin Rotaxen are loudly ringing the doorbell. And those prepared to spend big bucks on good looks will not go for a Cessna anyway.
The C152 is in my observation a poor alternative to today's LSA's, mostly single Rotax powered. It does make a solid rugged trainer, OK, but so does (to name only one that comes to mind first) the Rans S6 Coyote. And that one is cheaper to acquire and cheaper to operate, in most places.
Cessna saw good reason to explore the new C162 way - the C152 was no more going anywhere. No wonder, of course, after all those years. It has been a very fine aircraft in its day.
If the C162 hits success, we may hope to see a "next generation" C172 next. It had better be diesel powered from the beginning.