Everything including the Kitchen Sink
What Allan and his guys are doing is expanding within their niche. They have supplies for all sorts of bathroom related products already. They have relationships with Kohler, Whitehaus, American Standard and the like already. These manufacturers also make kitchen products. So what they're doing is expanding into a new area without setting up new vendor relationships. They're selling Kitchen Sinks and faucets at a new website - appropriately named buykitchensinks.com. So now expanding within a niche starts to make sense to me... building into another niche with products that are related but not quite the same and through the same vendors - at least initially.
Expansion with Minimal Risk
So as we start looking at some expansion plans, I'm going to use the advice of Shoemoney and use Allan's example to figure out how we can expand into new niche markets with minimal risk and initially using the same vendor relationships we already have. Thanks to Jeremy and Allan for helping to give me some ideas about future direction... and watch out those of you in tangent markets. We're coming.