Yes, bitcoin needs a metaphor makeover.
However, from personal experience I think your just as well off getting a really good UX guy/gal to sit down and design the interface as you are going through a usability lab, and it's a LOT cheaper. This is, of course, just my 2 cents, but I've never been much of a fan of a lot of formal usability testing (and I've worked in 2 usability labs for different departments with full kits - one way mirrors, everything recorded and transcribed, mouse movements, eye tracking, etc etc). Just get someone, or someones, who really know what they're doing.
Maybe you can start thinking about various workflows and corresponding metaphors and note them in this thread?
BTW if you do some searching I recall seeing other threads trying to tackle the interface. They even had mockups of the design.