I know more testers on incoming are always welcome, especially if you have a bit tenacity to also try and resolve/workaround the problems you find. Contributing there would be much appreciated I think
There is also an online chat for Linux Mint, you may want to hang out there also. Just open XChat from the menu and you will be automatically connected to #linuxmint-chat (general chat) and #linuxmint-debian (support with other LMDE users).
(Gnome 3 Shell fork, developed by the Linux Mint team) will be coming to LMDE soon also. Cinnamon is heavily under development and there is a call out for developers to work on applets and extensions to give it more functionality. There are a lot of request from users on new functionality, like here
(that one would be a good project to get started with, as you can take the existing Gnome applet and rewrite it to a Cinnamon applet).