I've just had an advertising flyer from a company I've bought electronic components from for years, and for once it looks quite interesting. It's bit expensive, but looks to be re-usable, so might well be cost-effective if refining a design using scale models. It might well have a resale value, too, within the self-build community.
I built a total of six 1:50 scale models of our house, at a cost of around £50 in materials (foam board, liteply, cutting board, glue etc), so maybe the cost of these kits isn't all that high, given the possibility to re-use the components.
I'm not endorsing this at all, as I've only had a quick look at both the details from the supplier and the manufacturer's website, but it looks like an interesting system: http://arckit.com/