A winning bid, is a bit to purchase as far as I know. The only way a winning bidder could turn up and not buy the vehicle is if he thought it was not as described in the advert.
You just need to add a significant amount of detail to attract the interest of anyone looking for such a car - which it seems you have done. You get much more exposure on eBay than you can on Autotrader or Pistonheads and you can put more pics and more text that you can elsewhere.
Yes you would ideally expect someone who is actually really interested in buying the car to make contact with you. You also get numpties wanting to px with a Ford Focus or something...or offering you a fraction of your asking price
The only things I would do differently (...well you did ask is not have a 'Buy it Now' since people always like to negotiate on price. Car buyers tend to feel that have got a good deal if they can knock a couple of hundred quid off a price... even if you had inflated the price to counter that in the first place (!).
The other thing I would do is try and put it in an alternative category such as 'sports cars or 'convertibles' since someone who is not being marque-specific might not see the ad (say they were looking for a BMW convertible, but thought your car looked good). You also have to be prepared to re-list it for a few weeks until you do get a buyer from one place or the other.