I have a friend who uses a dodgy copy of photoshop CS2, it's fully featured and does download updates fine so yours probably would as well. Having said that, if you're going to use the software as much as other photographers do then you should really buy the full version. Why not trial the one you have at the moment and use it to decide if you want to pay for the full version, then you're morally in the clear
I must say that I found it a bit annoying to see my mate using a free, fully featured version when I'd forked out a ridiculous amount of money on the original!