There is definatly a market for it.
We do a lot of gutter cleaning, but some/most of the gutters we get to do would not get cleaned using a pole system , invariably they have large mounds of grass, or small trees growing out of them. We recently had a sapling growing with 3ft roots going into the tiles!!
The other problem with using a pressure washer is the mess it causes, if the gutters are already blocked, the extra water you are putting up there has nowhere to go but over the side and down the walls, onto the windows.
You need to be able to see what you are doing, where the blockages are and if you have got it clean. There may be a tile slid into the gutter blocking it, or a lump of cement. These need to be physically removed, not just washed along.
The tools you will need are, good long ladders, ladder stand off with hook attachment, bucket, trowel, drain cleaning rods and half moon attachment, cloths to wipe down whites, hose and water supply to rinse out gutter at end of job. Standard house front and rear gutters, wipe down fascias and soffits - £80 - £100. Time taken 1-2 hrs.