If your really going to be serious in taking it up full time then yes it is worth it but imo I wouldn't call myself a professional tiler after a 4 week course, yes if you take your time set yourself a good standard by the time you have finished the course then I can't see why you can't earn a living from it. I did the 4 week course and the thing you really need to get right is your setting out, get that right and the rest comes easier.I have a number of jobs lined up for people I know and when I went to give them a quote they didn't realise there was so much prep work before you start tiling.
Just bumping some of the tiling tools related threads. This thread might not be current discussion, if it isn't, just ignore this, and it'll soon drop off the list. Don't worry if you bring it back into current discussion yourself though, the content within it could be useful for somebody. So feel free to add to it if you have something valuable to add.