"Even if your cylinders are in good shape, is there a benefit to boring?"

If they are not tapered or egg-shaped, you can do a down-and-dirty rebuild by honing the cylinders to remove the glaze which has formed on them and to provide new cross-hatch marks in the bore so that the new rings and the bore can have a chance to wear-in together and putting new rings on the old pistons and re-using them. Putting new rings in the old (smooth) cylinder (not honed) will not allow the rings to wear-in properly and the motor will not seal up properly. You have to determine how much the cylinder is worn when doing this, because if it is worn too badly, you'll have excessive piston-to-cylinder-wall clearance and the pistons will rattle in the bore because they are "loose". Boring the cylinders larger and using larger (oversize) pistons provides a brand-new surface for the rings to run on and insures that the bore is not tapered or egg-shaped and increases cubic inches at the same time.

"I suppose I can also deduct that it is of benefit to get a crank with a long stroke if I want to add hp?"

yes, to add cubic inches and thus more power from the same motor.