Iceburg 1,
While it is now true you can be a SEP instructor and earn money without a CPL, just like a microlight instructor can earn without a CPL, as an SEP instructor you would need to be part of a FTO (used to be a Registered Flying School).
Unless you want the paperwork and hassle of setting up a FTO - you can't set up as an RFS anymore - then the big advantage of the microlight route is you can start your own school with limited (almost no) paperwork.