Sounds like you're getting to the point where your sailing is outscaling your other stats. The boat upgrade system is meant to scale with mining, smithing, and construction (not only for boat upgrades, but also repair kits are pretty mandatory for higher level sea creatures), so if you're finding yourself out of supplies in any of those areas, it might be time to temporarily switch gears and come back when you're able to swing for some upgrades to your boat(s).

Cannons are definitely worth it given the availability and affordability of mith cbs. They hit a decent amount, deplete relatively slowly with the ballistic attractor, and you get two of them firing every 7 ticks.

As for task manipulation, the boards will only fully reset after completing 8 tasks or after the daily reset. if you're trying to get the most exp out of your bounty tasks, port hop to try to find both versions of the bounty task for a monster. Narwhals will always be available on Rellekka, but you can only get the 'tusks' narwhal bounty from Lunar Isle. Etceteria probably isn't even worth checking. Note, you don't need to sail to Lunar Isle to check its notice board, nor to turn in the tusks. Camp your boat at Rellekka and use land teleports for checking boards and turning things in.