Missing a lot of options from Finder's right click context menu

From your question it looks like your Dropbox is misbehaving.

Do you have the latest version of Dropbox? Reinstall Dropbox with the newest version.

Dropbox uses a "hack" which extends the Finder (in an unsupported way) to provide this "sharing" link. Because these "hacks" can cause crashes, Apple tends to disable them when newer versions of OS X ship. There's probably a newer version of DropBox that gets around these restrictions that you'll need to download.

^{Source: https://discussions.apple.com/thread/5577081}

Will, are you using TotalFinder? I had the same problem and it was caused by TotalFinder. Upgrading to version 1.6 solved it.