Given sufficient funds, how many partly-completed builders would buy a flying RV until their project was done?
I can't speak for the population of builders but in my case I'd buy an RV-3 to fly while I'm working on my 9A. It isn't money so much as it is my commitment to staying married that's stopped me.
Do you think you'd finish your project if you did?
Yes. But there's a point worth mentioning here and that's the 3 and the 9 have different missions and I'd like to do both kinds of flying. If I were to buy a 9 while I'm building a 9, well I'm not so sure about how that would affect my ability to finish.
Would it diminish the satisfaction of the build or the excitement of flying it?
I don't think there's much that can diminish the satisfaction of building but it clearly isn't something for everyone. It is hard for me to express how much I've learned about aircraft, especially GA aircraft, as a result of this build. I've owned a Cherokee for more than 10 years and while I did a competent preflight when I bought the plane, when I look at it now, I see and understand sooooo much more.
As for the excitement of flying it, I assume you mean the plane you build. I can't imagine flying another RV will be the same as flying one you build yourself. I can see where you'd be much better prepared for flying the RV you build yourself, if you have many hours in another RV.
Would you buy the same model?
No. I've already answered this one, I think.
Would you get similar or less creature features?
Definitely fewer. If I were to get a 3, it would be a minimalistic day VFR plane. I really have not thought too much about it but I could imagine a panel consisting of a TT Gemini PFD, an SL40, and GTX 327 and the mandatory gauges. If the Gemini EMS met that requirement, that would suit me.
The 9 I'm building will be very well equipped; night IFR legal and have enough redundancy to satisfy me.