I've felt this same way for a while, I've been running a used car site since 1995 (http://www.ausedcar.com). The sad thing is I've experimented with all sorts of other ways to search for cars over the years like what you are recommending (in the past I've let you search by fuel economy, etc...) but nothing seems to convert (ie work) as well as the same convention everyone else uses of Make and Model :\.

Also Craigslist will probably shut down the linked site soon, it's quite unfortunate how Craigslist essentially took the entire FSBO car market, but won't innovate in the way that this site shows it could.