I agree, Flamenco's faceted metadata is a great way to look at structured data. But Solr has facets, and they're really easy to enable. So that kind of functionality is not really the hard part.

The really tricky part is finding out what your users need (which is of course not what they say they need).

Use your search logs: the most important part is seeing what they search for and especially if they have zero results. Talk to them about why: they may have different vocabulary or need something new, or it may be OK because they're checking for the absence of something. You can also look at what are the top queries and the top kinds of queries: maybe they really want to segment by assembly district: that's a great use for faceted metadata.

Then you can use the standard UI tools like sketches and wireframes to expand the search form for their needs. They may want to search for nicknames or maiden names, who knows? I don't, but they do.

It's an iterative process involving content coverage, back-end search functionality, and client-side interfaces, but when you do it right, it just hums :-)

I agree that the Google Box is closed, but as I understand it, there is no ongoing fee, except for support. You buy it, you own it.