Steve,
We have exactly the same garage size as you do, and four cars too! Our solution was a Perfect Park 7000 from
Lifts Unlimited. Believe me we looked at everyone out there before settling on this, we even drew the outlines of all the lifts on the garage floor! Our Ginetta G15 has a tiny wheel base and sits comfortably on it. The things that swung it for us were the fact that we could put either the British cars on it or the minivan and work on them comfortably and safely; all the pully's and cables are inside the columns, and there's a dust cover too; the unit pulls centrally down the columns and is therefore incredibly stable (it's not bolted down, and doesn't need to be) - from what I remember of our research the others didn't work in this way, they stress the columns which causes the top of the columns to want to pull inwards during lifting. Not only is this more taxing on the components but also makes the lift very unstable. They will also supply the ramp with just about any type of power setup you can think of, which was great for us, as we won't always be living in the States (we're English). They usually have a sale in the fall too.
Not the cheapest out there, but definitely one of the best engineered solutions available for the "hobbyist/collector". We're very glad we bought it.
Here are some real life "action" shots!
RG /ubbthreads/images/graemlins/england.gif