I really don't think the 300 WM has that much kick. You have a lot of overlap in your collection.
If you get the 300WM I'd consider getting rid of your .30-06.
I'm not a fan of the WSM cartridges. On paper they look great. Once you put them on the reloading bench they leave a lot to be desired. I also don't believe they'll stand the test of time.
Tom