The 300 WSM is a good cartridge, no doubt about it. I think, however, that the '06 does about 95% of what the WSM will do and do it generally at lower pressure. The '06 is probably the most nostalgic round in North America and because of its war, hunting, and target history will always have lots of fans that love it for more than just ballistics. Just based on ballistics, the '06 is always a good choice for almost any North American hunting and a lot of African hunting too. If you load up an '06 with RE 22 and a 180 grain bullet you're likely to get over 2800 FPS with a 22" barrel. The 300 beats that by maybe 100 to 150 FPS (with more recoil) but as O'Connor (or somebody like him) said "I doubt the Elk will tell the difference."
Go to any rural supply store in South Africa, Namibia, Australia, or Germany or just about anywhere else and you'll find 30-06 ammo on the shelf. The 300 WSM? Not so much. The '06 has way too much of a head start and the 300 does not offer anything radically different for it to ever eclipse the '06.