I think your being a little harsh especially with regards to the comparison to the Montego and Meastro but respect your opinion...
Besides the front boxter type lights, they look alot like the 997....
I think the C4S, with its turbo wide body and without the rear quarter intakes and turbo spoiler look super nice...
I suspect the earlier 993's holding their values the way they do is down to the fact that, yes they are pretty but more importantly they were also the last of the Air cooled 911's...
997's were an obvious step up from the 996, especially as Porsche were into their second generation with water cooling....
Interior wise, the 996 was a let down admitedy and Porsche learned their lesson with the 997 thank god...
The 996 Porsche 911 Turbo WILL go up in value, and hence is still a supercar bargain atm....
I remember 964 values remained low compared to older and younger versions for many years... probably also down to styling (compared to the 993?).... but they have picked up hugely over the last few years... Not sure about all 996 models but the Turbo being the Turbo, will definetely pick up and i cant see them getting any lower.....