I'm using Dremel 3000 along with a diamond wheel which is not cheap either at around 20EUR. It does the trick for about 30-40cm and then goes dull. It only cuts when the dremel is at it's highest setting. Anything less and it barely scratches the surface. It seems as if when the resin is heated while cutting, it sticks on the wheel and dulls it. I don't know if that's whats happening but I can see that the dimond wheel is covered with thick black stuff. I can sand it down with some abrasive paper but that doesn't seem to improve anything. Can anybody help me with that? Any methods for cleaning/sharpening the diamond wheel? 

Have to agree with the perma grit stuff. I bought the small sanding block and mini cutting wheel a while ago. I´ve only used the wheel once so far but it cut really easy. The sanding block however has built 2 kayaks and paddles completely. That includes sanding/shaping plywood, sanding fiberglass and carbon and even for the fairing. Plus it´s done other bits and pieces around the house including sanding aluminium door frame. It still works as good as new! I can´t even guess at how much sandpaper it has saved me.