I suppose real value can mean different things. I think you're referring to actual monetary value on the market if you decided to sell the car. I'm never going to sell my car, so I don't think about its monetary value. I guess if you buy pre-built cars or pay people to build/enhance them then you definitely have to consider actual street value because chances are you'll sell it one day to start a new project or buy a different car(which, btw, is totally cool in my book). I had a guy in a new Gallardo convertible pull-up at a small car show in Encinitas and tell me that he has a large collection of cars and that he loved my car and wanted to buy it. I told him it wasn't for sale. He said with a smile, "Are you sure about that?". I said, "Absolutely sure", and it felt damn good to say that(and then go home and eat some Ramen noodles). It doesn't matter what he offered me, I would never sell it. I spent nearly every day of 3 years of my life taking that rust bucket apart and putting it back together new, never handing it off to anybody to do any work on it other than apply the sealer coat and blue. It basically defined(robbed me of) 3 years of my life and it's an accomplishment(rare in my life) for me that I just could never let go of. To see someone driving off with all my hard work would be a shot to the 'nads I would never recover from. So I'd say most of my car's real value to me is based on 'pride', and the preservation of my 'nads.
Building a 300K car by DSE? Wow, can't wait to see that one.