I have an unused diamond shovel with silk touch 1 on it and I need some opinions of what it is worth.
I think most people like the new enchanting system, but sadly silk touch has almost become a junk enchantment. Besides grass and mycelium, I use silk shovels and axes for tearing out stuff like glass and save my silk touch picks for mining. If you can't get a price you're happy with, I'd just save it for that.
Another use would be to use it for Glowstone. That is assuming that a shovel doesn't destroy it. Pretty sure I was using an axe for this at one time though so I'm guessing a shovel would work too.