Chris, it isn't that the car lacks anything. From my perspective, it's that I already have a Speedster in the garage. In fact, I wonder how many folks here were directed to this site by folks who already checked in here saying, "Hey, Dude, check THIS car out!"
Your car is one of the most beautiful Speedsters ever. Have you considered asking Henry if anyone's looking for such a car and maybe can't afford the benchmark he would set to build one? Maybe he'd put you in touch with a buyer.
Otherwise, exposure in a catalogue (Hemmings or some such glossy, photo-packed pub) might be a better way to go with it than eBay. There's a market for that IM of yours, believe me. You need to aim it at the recession-proof folks who want it in the fifth or sixth bay of their garage.
Don't sell that emerald beauty short thinking this site is the end-all, be-all.
Also, try taking your photos within a half-hour of dawn or dusk. Photographers call that the 'Golden Hour' -- and you can use it to highlight the green color with a little golden overtone. Less blue reflection from the sky and a little more yellow-gold from the setting or rising sun on the paint will make it pop.
Make sure the sun is ALWAYS behind you and your shadow is out of the frame -- and consider the use a fill-flash instead of a direct flash for mid-day or afternoon pictures.
Most cameras nowadays will let you de-select the flash manually, and as long as you hold the camera still (tripod), you can take the one evening signature shot you need as the attention-grabber. Once you've got my attention, you can ease up on the creativity to show me the details.
Take the shots from roughly headlight-level, with something off the beaten path as the background. An odd building, or maybe something nearby to you that's specific and unique -- but that you'd have to drive to get to. Give the car a little lead-room, also. Give it a little space so my perception is that it wants to drive across the frame a little before it starts to leave the frame. Close up the gap behind it, but don't clip the bumper off.
If you vary from the car's height, make it un-naturally high and give me the reason -- the car's in a garage, a barn or someplace else interesting that makes me want to look closer. And for Pete's sake, turn the lights on! Give that old-appearing mechanical beastie a spark of life; two-dimensional, dead-looking cars are uninteresting.
As Walken said, "The eyes ... are the windows to your face."
Have a look at some of the better advertisements from the Porsche ad-shack over the years, and emulate them as best you can. Quality images will help you find the market segment you want. And sell the car in four words or less at the end of your ad; "You want this experience." (or some such. Push the BUY button for me, don't leave me the option.)
Make me want to OWN the car to get to someplace I'd never get to see otherwise. Here are my best examples of what I'm trying to describe:
