The beatmix is good enough to make it your controller for several years. Depending on the genre you want to drive.
There is no need to upgrade to any pioneer gear (though their highend DDJ-SX for example is very good), there are several good controllers also high end that are equally good and need to be considered later.
The Wee-Go is really a fun toy. It is totally cool if you DJ at home in the bedroom, but it can also be cool when you are already a well versed DJ (who knows all the basics) and want a light portable controller, just to fool around with or make a garden party at their house.
Friend of mine actually has one hooked up when he does his house parties, but he plays with his VCI-400 and has the WeeGo if someone of the guests wants to try around a little (like open mic hour), for which the VCI is much too complicated.