regarding low mileage being a factor, it is, to anybody who understand materials. the chassis flexes each and every time it is driven. this results in metal fatigue over time. you can tell the difference between a low mileage chassis and a high mileage chassis. it's easily discernible in the rattles and squeaks. yes, there is an argument to be made that a certain number of miles should be put on the car regularly, so as to maintain flexibility in rubber, and seals lubed, and such, but that only requires about 1000-1500 miles a year.
regarding how much to spend, an average 98k cab will only get about $13-15k in any of the standard solid colors, a bit more for a metallic, and a bit more for the rarer colors. a similar hardtop would get about $2k less. a well maintained version will get about 20% more, if there is documentation. you'll get about half of the amount of money you spend fixing it up, if it is done less than 3 months before the sale. so, you have to balance that one against the cost for the work.
a car with between 60 and 90k will get about $2500 more. a car with between 40 and 60k will get another $2500. a car with less than 40k on it will get upwards of $19k
interestingly, porsches garner a lower price if modified.
these are all private sales estimates. auctions are an odd anomaly. sometimes they get more. sometimes less. it's a bit of a crap shoot. the private auctions tend to vet the cars more, so there is a tendency for the price to be higher, and often unrealistically.
94 Midnight Metallic Blue Cab Porsche 968 w/deviating cashmere/black interior and WAY too many mods to list - thanks to eric for creating
www.968forums.com
"It isn't nearly as expensive to do it right as it is to do it wrong."