The question as to whether IS is worth it or not really depends.
For me, it wasn't. I have the 70-200 f/4 L without IS. I haven't regretted it at all. Of course, I don't photograph wildlife and I always have a full-sized tripod lashed to my pack (for bracketing problematic exposures, waterfalls, panos, etc.) I don't miss the IS in the least, so the extra money wouldn't be worth it to me.
I know that you shoot a lot of moose. If you find yourself doing this at long focal lengths in low light conditions without the chance to break out a tripod, it may very well be worth it for you. $600 worth it? Not for me, but maybe for you.
As for turning off IS on a tripod, this is direct from Canon:
"The IS mechanism operates by correcting shake. When there is no shake, or when the level of shake is below the threshold of the system’s detection capability, use of the IS feature may actually *add* unwanted blur to the photograph, therefore you should shut it off in this situation. Remember that the IS lens group is normally locked into place. When the IS function is active, the IS lens group is unlocked so it can be moved by the electromagnetic coil surrounding the elements. When there’s not enough motion for the IS system to detect, the result can sometimes be a sort of electronic ‘feedback loop,’ somewhat analogous to the ringing noise of an audio feedback loop we’re all familiar with. As a result, the IS lens group might move while the lens is on a tripod, unless the IS function is switched off and the IS lens group is locked into place.”
I'm not sure if that applies to a monopod since there may still be enough movement to make it worthwhile. I'd take some test shots with IS on and off and compare the two.
And I'll third the B&H recommendation. You generally pay slightly more there than at other places, but the piece of mind is worth it. Photo gear is their bread and butter, so if you have a problem, you will be dealing with somebody that knows what they're talking about and will bend over backwards to fix it.