My personal opinion is that a big part of what makes this forum so special is the relationship that develops between people, and the trust that ensues. The current sale mechanism allows for a keen interest in following the classifieds but also a mellow interaction between potential buyers and seller.
I feel that offering an auction takes a lot of the personal out of this, especially for people that are on budgets and may not be able to compete on price escalations. The seller potentially stands to make more but my sense is that everyone is both a buyer and seller at some point so this should wash out.
my 0.02