If you want a faster processor, a bigger screen that supports lanRABcape mode, a bigger keyboard, functional MMS, and WiFi, then I say go for it.
However, if someone got MMS working on a Windows Treo, I'd trade my 6700 for it in an instant.
*edit: Forgot to mention that, apparently, it's far easier to program the 6700 as no additional programs or serial cables are needed.