I appreciate your comments. I like the idea of option number two, because it still gets to the end goal--a sale. It'd be a bigger project than I want to take on, though.
Option number three gauges interest in a scientific manner, but assumes that interest is a valid proxy for the end goal of a sale. I'm not sure how true that assumption is.
I've window shopped homes that I had no intention (nor capability) of buying. My employer one had a record day because one of the homes on the site was a football player's and had gotten mentioned in an ESPN blog. In both cases, interest was only vaguely related to purchase capability.
Testing all the way to the end of the funnel (home sale) is key, and difficult.