The practical question, of course, is "what practical solution is there?" Obviously we have a wide variety of views on this, from what's already been said, but I think we'd all agree that avoiding damage to the site is the priority, and the leaving of offerings that don't readily decay is a close second to that.
Chopping things down isn't a long-term solution, even if it was practical or desirable. I expect next time I'm at Long Meg there'll be things tied to the other trees/hedges in the vicinity. Notices from English Heritage might help - if well-worded - but that depends on their being read and heeded.
However things are done, it looks like the leaving of offerings is here to stay and trying to ban it would be counter-productive.
It seems to me the most productive way forward would be to join a few neo-pagan discussion forums and calmly and rationally suggest that biodegradable offerings would be much preferable to the kinds of things being left now. Ideas take root if presented in a congenial way and with frequency. This may not work, but I think it's worth a try, and I'm intending to do it. Those of us with a deep antipathy to anything new age, neo-pagan or whatever will need to proceed with caution, or hang around at the back. :D
I'm also thinking about selling biodegradable paper/cloth slips that can be written on and hung onto a tree or bush with minimal damage. Somebody, at least, could do with looking into that.
I think saying that removing things to "restore" it to how it was intended is quite an assumption as we dont have a clue what these things are for, although we can guess they wern't leaving pottery cows or metal toys...
:)