well....i think DW is a great utility and one that should be in just about everyone's toolbox. having said that, it may be good "preventative maintenance" but i don't believe it'll do anything about speed.
as for the intel aspect, well it is too early to know all the details and if Alsoft will charge for the upgrade or not...i assume they will update the software for the intel move. keep in mind this software is geared towards the *file system* and the processor that is running it is not as big a part of the equation (granted i am not a programmer/expert on this subject either).
in general though, i suspect that quite a few software vendors will time the release of their intel versions with their other "major upgrade/version" release plans so they can give people something more for their money than just a version that works on intel macs.