RE: Outhaul kit for Naish Sprint 7.3
Yes, yes, and yes. Adjustable outhauls make every sail better - I use them on everything, including wave sails. You'll extend the range of any sail by being able to tune it on the water, and you'll learn better where it performs for a given wind strength in its range. Plus, no coming in to the beach or jumping in the water to retune your rig.
For smaller sails (<5.5), you can always just use one boom cleat, to cut down on the clutter. If you're sailing in waves, have the cleat on the 'going out' side, so you can bag the sail for more power going over the waves, then tighten it up before you jibe/tack, to depower the sail a bit for the wave ride.