You might be right to some degree, but I think you're oversimplifying it.
1) Flight schools are struggling universally these days--I see that more as a function of the economy than it is the equipment the school uses. I see schools hurting regardless of the equipment on their flight line.
2) There is a *lot* more to the "$4k" quote for a license than the "$9k" quote for reasons beyond simply the aircraft rental price. It's basic math. Let's say a person spends an extra $50/hour on the aircraft. For 50 hours of training, that's $2500 extra. You're quoting a difference of $5k. Where'd the other $2500 go? Higher fuel, insurance, instructor rates, etc. Times have changed in many areas beyond just the aircraft.
3) The price difference between $4k and $9k is relatively minor in the whole scheme of things. In the non-commercial, recreational demographic, we're competing against motorcycles, jet skis, RVs, vacations to the Bahamas, etc. Somehow people find ways to afford those things. There's no reason they won't put their income in to flying if they see the value in it. The problem is that as an industry, we haven't done a good job of showing the excitement and value to getting one's private pilot certificate. We keep trying to compete on price rather than value--in my opinion, a recipe for failure with any business other than Walmart. I agree it's hard to convince people to give it a shot, but that's because they don't see the value in flying, not because it's $5k more than it was 10 years ago.
4) New aircraft are going to be more expensive than used aircraft, period. I suppose a person could argue for flying only used aircraft, but that's a whole other argument. If we limit ourselves to new aircraft and only have to pick between glass and conventional panels, we're talking about maybe saving 10% or 20% off the total purchase price. That's only going to drop the rental rates by a few dollars per hour.
See how there's a lot more to it? It's easy to blame glass panels for the demise of general aviation, but I don't think that's reality.