I have considered the '93-94 Carrera 2 and 4 from the 964 series, and also the '95 993 series. I would rather not go any lower than '92 or '93 simply because I have been reading that there were a lot of updates and added gaskets to once gasket-less parts of the motor post-1991. ALso, I would only buy a Carrera.
One of the reasons why I am considering a 911 in the first place is for resale value, which still seems to be very high in the 964 series since they're known for their great reliability, though I bet you're right in saying that the 993 series has an even better resale value since it's newer, more sexy-looking, and there are less of them.
That said, I can't lie by telling you that I wouldn't go for a good, low-mileage 92-94 Carrera though. Even they, as old as they are now, have much better resale values than 95% of production cars that I know of.
I'm not dead-set on a Porsche yet though, I'm just kicking around the idea and trying to find out as much as I can about them. I actually have a couple other reliable sports cars that are much newer (C5 Corvette, Supra Turbo, etc.) that I am considering as well, but whose resale value, desirability, is not as high. Problem with the Corvette is that I need to drive it in the winter, and while the active handling of the Corvette makes it a dream to drive, they're impossible to get snow tires on due to how wide the wheels are. I still have to look into that though, but I know that if one were to put thinner, deeper-treaded tires on a C5 with active handling, etc, it would be a damn good winter driver for a rear-drive car.
My next car MUST be rear- or all-wheel-drive. No more front!