I'm curious as to why you'd want the 400 f/2.8 over the 500 f/4 if what you shoot is mostly birds. Obviously the 400 is a great lens, but for birding the 500 is really the ultimate in terms of focal length, size, and cost. I have a Wimberley Sidekick (works fine with the 500, wouldn't support the 400) but am seriously considering the full Wimberley head.
And I see nothing wrong with being a lens enthusiast! We can love the activity of photography and also enjoy gear that it involves. There's no rule saying you can't do both. You people who are worried about phraseology need to get over it - maybe you should be out shooting pictures instead of spending time with us "enthusiasts" on the forums!