If you're just looking for a really nice car to drive, then I personally don't think it matters at all what it started life as, as long as it is what you want now. As for values, I really can't get why a drop head is worth more than a fixed head. I know people who simply wouldn't have a drop head, so for them a fixed head would be worth more. It only makes a difference when you get in to this 'matching numbers' nonsense.
To me, If the car is what you want, go for it, if not, move on to the next one
If Lotus hadn't given them different type numbers, I wonder how many would be able to tell a chopped fixed head from a factory drop head?
Same goes a bit for the difference in value of a series 4 Vs a Sprint. With a few small engine mods, a couple of stripes & a bit of paintwork, a series 4 becomes essentially exactly the same car as a Sprint, Lotus even done it themselves. If you only want to drive it & have fun, is a genuine Sprint really worth ?10k more? Do you get that much more fun out of it? Again, to me it only matters if you are looking at it as an investment that will give you maximum return, & there are probably better things to put your money in if that's what you're after
Tim