I'm not sure if running dropbox traffic through Tor, at this presents as an option about 3/4 of the way through, is "friendly" to the Tor network as it currently stands. If my goal were merely to protect my IP from being disclosed to Dropbox, I'd probably just use a VPN.
I think your idea of what traffic is friendly to Tor is too limited. Traffic like this improves the anonymity supplied to users of Tor who need it most. The more traffic runs over the Tor network the better.