The only time we've been successful actually catching a fish while sailing was in the Caribbean. Dragging a line on a bungee behind the boat, we once caught a 40lb Mahi Mahi at about 9 knots.. At other times we've caught small tunas in a similar fashion.
Here in the PNW we've had little success but partially through little effort. For us how 'near' to our boat we get fish depends on how far away the fish sales dock or fishboat is
I do believe it's more cost effective to buy fish off the boat than buy the gear and run the risk of getting 'skunked'... or losing said gear for naught.
But plenty of people hereabouts are very successful prawning and crabbing, others do well leaving the anchored boat and bottom fishing or trolling at nearby likely locations from the dinghy.
Seems to me fly fishing and even casting would be problematic anywhere near a sailboat rig ...