Wow, broad question, depends on what you need and what you have basically,
I find that LE4 isn't very limiting, but I do find if i need to do anything on another system its a pain, if you upgrade you get a lot of the new toys that come with 6.5 and a lot of them can be handy, but you shouldn't really run into many problems you can't overcome in 4 with the right care. Giz a little bit of info on what you plan on doing and i'll try help.
I'll be making the upgrade soon