Indeed, a series of rolling blockades across a nations ports would throw up all sorts of issues to be dealt with. And it doesnt have to be necessarily targetted at any one nation : the 'prize' is the toll and plunder on trade if you win : for the popular trade ports, that could be substantial gains over the blockade period.
I also think we should not over-state the 'spam howker fleet' tactic : an easy and effective counter, and not that much more expensive, would be a swarm of cutter fleets : which gives the main problem for both attacker and defender : how far can you escalate the power of the fleets before it all becomes far too expensive to contemplate?
For the bystander, not involved in the fight, as Haron notes, rich pickings in plundering lit-up fleets of both sides are a most tempting prospect once the initial battles are over. Its win-win for them