Vw Heritage is awful !!

No worries.. the reason for parts becoming obsolete is down to a number of factors.
Mainly, car manufacturers only have to produce parts to last 10 years or so after the final production of a model. After this time some parts sell out quick - body trim, wheels etc due to accidents and being used to modify lesser models etc, other parts- cylinder heads, glass will sit in warehouses gathering dust.
The VW Classic Parts programme has put a lot of these parts all in one place, which is great news.
The other thing that they do is recommision obsolete parts, something the dealers would never of done  - Mk2 Golf G60 arches are a prime example of this.

There are a number of companies, and enthusiasts who have struck gold and stocked up when dealers have had a clear out - we are yet to "get lucky" with a situation like this - but this is simple business, and if many of us were given that opportunity we would consider it.
The other thing is, you have to be cash rich to sit on a pile of NOS parts waiting for them to become more valuable -many parts suppliers rely on parts coming in and being sold on in quick succession.

As for parts prices going up, as the cars become older, and so availability of new parts for them becomes harder to find, naturally the price asked for a genuine NOS item goes up too. This is reflected well with Karmann Ghia wings - in the early 90's we used to sell these every week at £200 per side. Now you can't get them at all, and people pay £1000 per side when they can find them.

Hope this explains a bit more

Andy