When it comes to older, modified cars like these, the people who are willing to consider paying top dollar are going to be evaluating the entire package. You might find someone eager to own a low mile, 100% stock, original owner car, and pay a premium for that, but I doubt these command the highest prices yet. On the other hand, one could have the most methodical, bulletproof, white glove powertrain, but if the interior/exterior of the car appear less than pristine, it's just not quite there.
I suspect that the cars which will command the highest values (even relative, given the economy right now) will be the ones with light mods which reflect insight and careful consideration to every aspect of the car. People aren't paying $10,000 for the mods. The mods under the hood will have to add value to overall package. The exterior needs to be sharp, clean, and free of defects. The interior needs to be well cared-for. No threadbare seats or halfassed short shifter installations. Clean carpets and headliner. All the buttons, switches and gauges working.
You want to spend $8000 building a 2.4L with nasty cams, a ridiculous turbo, and EMS, that's fine, but if your super badass race car looks like an otherwise neglected grocery getter from the early 90s, don't expect to get half your money back. Remember, NOBODY pays a premium for used performance parts.
I say it's about synergy. The whole package has to work together. If you've got a race engine, it needs to be a prepared car. Those are harder to sell these days, it seems, but that's your best shot. If you drive the car to work or school or just pleasure, invest in making it look - on the surface - like you're interested in more than just beating on it at the track on the weekends.
Just saying...
EDIT: I think Coop's car is super nice. I bet that, if he swapped in a stock long block with some mild mods, an E316G, sitting on about 300hp, he could relist the car, not say a word about how it was set up previously, and still get $8000 for it. Then he could list the up-rated performance parts on their own to get a couple grand more, getting closer to the goal of $12K. Downside to this is, what is the value of time spent working on the car to do all this, right?