My take from my point of view which is an owner of my first Porsche, 2007 997 C2S Cabrio.
A little bit of history, is that my previous car was a Honda S2000, which never ever had anything wrong with it apart from 2 well known issues which occur at some point and 1 is simple and costs almost nothing and the other was done under warranty. I think the reaction a while back of the dealer when I drove into them unable to raise the passenger window. The response was a look of disbelief that something had gone wrong. They came outside, someone pressed the child lock switch, and oh dear the window works and I get slightly embarassed. Point is, I am used to a car which does not ever go wrong and was very cheap to run with an expensive service being £225.
So, come to a 911 and having read the (over hyped I think) horror stories the car I brought had 3 months left of OPC warranty. I extended it, it is simply the peace of mind and ease of use if something is wrong (two things so far, amplidier being replaced soon and the coil packs have been done) that they come and get it, take it in, fix it, give it back, lovely.
Lets face it, if you have a 911, you are doing pretty well in life and sure some people, like me, run a business or have a hectic work life and the value of my time way exceeds any extra I give Porsche or whoever to have an OPC warranty over using an Indy, organising it, working out whats wrong, and so on which I would have to do without it.
Hopefully when I sell it it will make it worth a bit more and/or make it easier to sell, so I am happy to spend £1000 a year odd on the warranty.
As for prices, I think prices are linked to whats happening in the classic car market. My car is probably worth £32k to £35k at the moment, up to £5 more than I paid for it. You only have to look at the prices for some classic or rare 911's to see the classic car market is completely insane at the moment. A good example is a few years ago you could buy RHD Jacuar XK220's for £75k. Now, they are £350k. That effect is what is driving prices of any car which is or is heading to be a classic, and I think a 997 is a classic already. it looks great, drives well, and is affordable which makes it sought after driving prices higher, not lower. Ferrari 355's are another example, I almost brought one 5 years ago as you get a nice F355 spider for £35k, not they are £90k!
So, prices will be follow the classic car market, which is apparently slowing but seems to still be slightly growing.........