Sailboats are typically a displacement hull meaning they plow through the water rather than skipping along on top of the water like a planing hull. Displacement hulls have a maximum speed they can travel through the water so no, adding more HP will not get you back to the marina any faster. It will just burn more fuel
Just to be clear, you do want something with enough horse power to get your boat up to hull speed, or near it. That will depend on the boat and the engine combination.
One more thing, all things being equal, outboards do not perform as well as inboards in rough seas... in other words, when you may need them most.
Outboards can be less expensive, easier to work on and easier to replace if they kick the bucket.
More to think about....