I'm not so sure its always nostalgia that drives some of the prices, often classic cars are a way of hiding money and therefore investment opportunties are sort out as in every market place.......often such things like leading up the 50th Anniversary of the E Type, lead to increased demand and hiked prces, that then fell away following the anniversary. Cars that qualitify for Mille Miglia ie pre 1957 manufacurer versions eg Austin Healey 100/4 BN1 and BN2 will always have a greater following than later versions, basically for that reason.
Then there are cars that always seem to buck the trend eg the MG Midget....most people like the MIni had one at some point, yet their desireability and demand hence prices has always been low......there is a 4k miles totally original rubber bumber been on sale for years started at £13k and last time I saw it was going for less than £9k.
As for Morgan's, whilst their build quality has improved dramatically and there is less to be aware of and decreased likihood of needing chassis replacement etc in post mid 80's cars etc., they are definately struggling...........the higher maintence requirments of hand made cars may be putting people off. But compare the price of a Morgan with other brands in the market at the same price point and the Morgan seems a bargain by comparison.....but lack of boot, only 2 seats, hard ride may narrows the market considerably.