Stanley Lipshitz and John Vanderkooy at the University of Waterloo conducted a test a while back that concluded you could get away with loudspeaker cabinets that were relatively light-weight and flimsy as long as you had adequate bracing judiciously placed etc to make the resonances fall below their detection threshold. So, will the affects of bamboo really make an audible difference over 1" MDF if the cabinet is already braced properly? I doubt anyone would notice a difference, so don't get too caught up in trying to decide which is best. With that said, if you have the money then why not go with bamboo?
To quote Sean Olive:
"As long as the speaker enclosure is designed in way that its resonances are below the masked detection threshold (as Lipshitz and Vanderkooy found), you are throwing money at something that falls in the category of what Toole calls "audio jewelry." It may have no audible benefit, but being able to afford it makes you feel good about yourself."
Don't get me wrong, though - I love speaker porn! Sean is just saying you don't need a riduculously inert cabinet to prevent audible resonances, and I think it is safe to say Jim's cabinets are well made and braced.