Hello Pilk, and welcome to the forum.
Having just completed my year long search for my ideal pagoda, I have most of your questions still fresh in my mind. However, I am no expert here so I'm sure the more experienced members will chime in soon.
Here's what I can tell you in regards of your questions:
1 - The main "bad" thing to look for will be rust... other than that, I think the rest of the car is easy to asses.
2 - Desirability will depend on personal preference, but I would venture to say at least, that the Hardtop Only models are less desirable than the ones with a Softop; some people say that manual transmission may be more desirable than auto, but so far I was not able to see this reflect in pricing. 5 Speed Manual transmissions are very rare, that may become more desirable, as with every thing that is scarcely available
3 - Rust is probably the car's biggest issue. You can spot it behind the headlight buckets, the inside of the front fenders, on the floors, inside the softop compartment, inside the trunk, on the main frame rails and sills...
4 - I would suggest reading as much as possible on the car. Try to understand details on the car, specifically what model and equipment should it have.
5 - A reasonable price will be determined by your interest in the car. Keep in mind that these cars were built in large numbers, so there are many more out there than you think... I'd say that rust is the key factor to determine the final price of a car. A fair price range is between $25 and $35 K, below that, you're probably looking at major work on the car, above that, may be too much for just a driver/tinkerer
Finally, check out this link to be able to identify the color you're looking at:
http://www.sl113.org/wiki/DataCard/PaintCodesGood luck in your hunt!
Andres G