I just found myself in the same position (minus smog related stuff). I'd had my rx7 since 2004, and it had most of the parts I wanted in it already, and it was running and driving fine, just had a bunch of little issues that needed fixing. I didn't have the time or motivation to really make it nice so it had been sitting for almost 2 years. During that time I graduated college, got a real job, and moved into a house with a nice garage. I now finally had the money and resources to really make my rx7 into whatever I wanted, so what did I do?
I sold it.
IMO life is too short to get attached to one single car forever...there's just too much cool stuff out there, and once you have the knowledge and money to build what you want then why wouldn't you? I lost a bunch of money on my rx7 but I just don't care - I had a ton of fun building it and driving it and learned a lot, I could have pretty much given the car away and it still would have been worth it. I know my next project will be way faster and nicer than the rx7 probably ever would have been, and I now know exactly what I want out of the next car so I can focus on that from the get-go. For me the sadness of losing the rx7 is completely overshadowed by the excitement of the next big thing. So if you're not going to be 100% happy with the finished product, I say it time to move on.