Hello Andy,
Well, the september 2006 of 911 and porsche world featured a 993 buyers guide. You can order this issue by contacting the publisher or alternatively maybe someone can scan the buyer guide in for you. (You might find the above mentioned car featured there.)
Secondly, a link towards a US forum, regarding 993 myths and facts:
http://forums.pelicanparts.com/showthread.php?threadid=184193&highlight=carbon+AND+993
Finally, there are "The Books": for engineering types the Paul Frere reference work: "the 911 story" and to get a very very good overview with chassis numbers, engine numbers, specification, changes per model year etc etc there is Peter Morgan "the original 911".
There is no such thing as a cheap porsche really. There are always exceptions that a seller "needs" to sell due to family reasons or whathever. You might get lucky, but don't factor it in. Also, a contigency budget is wise. AND DO A PRE PURCHASE INSPECTION. Its the best peace of mind ever spend and you learn something about the vehicle in the process.
Maintenance is paramount and more precisely: maintenance with the correct mechanics. The 993 is a specialist car and will still be serviced by OPC's but you might find that a respected independant can actually do as good if not a better job. Brakes, suspension parts, tyres, clutches etc are all maintenance items and once again it depends on the service schedule and driver/ driver style whether they kept on top of things. High mileages, when correctly maintained, are not a problem- on the contrary even: they are barely run in at 100.000 miles. Rule of thumb is still: a well used porsche on a long distance run is happier than a car that goes from heated garage to OPC and back.
As you said earlier, the 993 is a great rational choice but it is a wee bit schizophrenic: on long distances it is rather comfortable whilst in a controlled environment such as on the track it is a mighty weapon. Also, it is lickely that the car is possibly more capable than you as a driver- professional tuition with a 993 is an eye opener. (I drive a 76 carrera 3.o but had tuition in a 993 RS back in 1998)
The lotus is a mean, fast and raw machine. The 993 is more plush. It feels solid and it is extremely capable whilst still offering a surprising degree of comfort. It is an absolute icon.
*edit* long post on pre purchase inspection:
http://www.pelicanparts.com/techarticles/911_prepurchase/911_prepurchase.htm
Best regards,
Bert