You're not aware that Debian Testing is now frozen since the end of June. That means nothing new is coming into Testing from Sid until after Debian 7.0 "Wheezy" is released. Once that happens, a torrent of updated packages will flood into Testing as the development cycle begins anew. Another complicating factor is that LMDE intercepts updates to Testing, ensures they're safe, perhaps patches where appropriate and then releases them in bundles called Update Packs. This policy ensures that Mint users enjoy a consistent, stable experience and Mint can maintain a modicum of control over breakages due to troublesome updates, which can happen when using Debian's Testing repository. I have it on good authority that update Pack 5 for LMDE is imminent and will probably contain the latest Gnome 3.4.x and an updated Cinnamon version. While you're perfectly free to change your sources to track Debian Testing directly, or even to Sid (Unstable) and thus receive updates more quickly, this will likely break your system if you don't know what you're doing. For example, the version of Cinnamon for LMDE is currently incompatible with Gnome 3.4, which was released to Debian Testing a few weeks ago. Furthermore, if you want to track Debian Sid, then there are distributions that are designed for exactly that (Siduction, Aptosid) and their communities will be in a better position to help you should things go awry. Note that most distributions who track Sid favor KDE supporting Gnome as an afterthought if at all. If you're going to switch to a Sid based distro, may I recommend Siduction as it's community is much friendlier than Aptosid's where many users act like arrogant pricks who like to condescend to users and bristle at questions from newbies. Steer clear!
AMD Phenom II 64 X6 1090T Black Edition Hexa-Core
8 GB DDR2 RAM
nVidia GeForce GTX 660
Linux Mint 17.1 MATE+Compiz
Kernel 3.18 Liquorix-amd64