But he asked for peoples opinions. I never liked everyone responding with "do what you want, its your car." Obviously, I can do what I want... but I asked for opinions for a reason.
Here is what I see on this situation. You havent touched the Z in forever and you said it yourself, that you like 510s more. It doesnt make sense to me to spend on this money on a project you dont really care for. I would do one of two things:
1. Just keep holding out for the right 510.
2. Possibly even sell the Z to add more money to the 510 fund.
If youre not really excited about the Z at all, why keep sinking money into it? It just seems like a waste. It scrape whatever money together that you could and build the next 510 the way you really want it.