So here we go...

I couldn't find a built-in API to do this in Idapython. All the built-ins required that the DLL was loaded by an executable. For my purposes, that wasn't an option. So if you want DLL base address on just the DLL disassembled in IDA, you have to pull in Segments() and just get the lowest one, or index [0]. That's how I did it anyway. Code on github shortly...