Well I went out and bought a VGA box for my DC. I don't think words can express the incredible difference. Being someone who doesn't normally notice slight differences, like that between 128 kBit and 192 kBit sound, I am very impressed. I had a spare monitor hanging around and have now added it to my gaming rig. Just amazing what a $15 box can do.
And I'd still like to know if there's an accessory that allows you to plug a PC controller into the DC. It's a regular old pin connector, not a USB pad. I haven't seen anything like it looking around, but then you never know.