The slow depreciation is not what it was. The "normal" 996 and 997s tumble pretty quickly these days. This does however mean that picking up the next one becomes a reality (although I keep putting it off). Real world example - mine was £19K in April 2010 with 60K on the clock. Today it would still be in 5 figures but only just - and that is because it is a good one - no crunches, no engine problems (not for sale). I don't really consider £9K depreciation over 4.5 years for the miles that I've covered to be at all bad, but it is all relative and the next one probably base to be younger than 2008, under 40K miles to make it worth swapping - and that is three times the price that I can get for mine. I will change one day, I suspect that mine hasn't got much further to fall if looked after (although I have heard of people with Boxters picking up a second one for spares - they are so low in value).
The important thing is that 911s today are more accessible than they have ever been. The old adage of being able to afford to run one still holds true though - if you are unlucky they can be very expensive. It's OK when the "non Porsche" part fails - but when it is a "Porsche" part then be prepare to dig deep. The water pump is a good example. It is a Porsche pump and buying an aftermarket one is a known mistake - so that water pump is going to cost you £600. This doesn't of course apply to those looking at air cooled ones - but neither does "more accessible than ever" - good ones are very expensive - poor ones are on the way to being even more expensive!
The 911 is the only car that I've owned that puts the smile on my face like the Mog does - there is just something about that pendulum swinging about behind you that is even there with the 991. A lot less scary than it used to be, but then again they're a lot faster too.