It amazes me that my GA rivals really don't seem to make an effect to get rid of cliche-ed stuffing-sticking-out-of-the-seats aircraft.
How old is the house you live in? Yes, I do see some houses being leveled to make room for new ones, but not on a regular basis. We don't raze a house because it needs a kitchen reno, and new paint, we invest in the house.
The fact that people choose not to maintain the appearance of older aircraft is not automatically a slight to their airworthiness, though I agree it's an indicator as to attitude. I have repainted, interior'd, redone the panel, installed new radios and zero'd one engine in both of my 1970's planes since I have owned them.
At a recent visit to an aerodrome primarily frequented by non certified types, I saw many really junky looking aircraft, some of which were seemingly abandoned - and I doubt any of them were as as old as 15 years.
The cost of brand new design and manufactured certified aircraft is too high, and a disincentive to investment for most "private" owners to be. That's sad. But to label all older aircraft as inadequate is not right either. My 1975 C 150 is worth twice what it's original factory price was, and I have paid fairly to maintain it in that condition. But on the whole, it has paid me a little to fly it 2900 hours in the last 28 years - one of my better investments!