I am two blocks from the Atlantic ocean, and have no weather resistant coatings, or wet look on my speaker cones, my system is in an indoor building and I have never had any problems with the cones weathering from salt air!
As for the " Wet Look " available from parts express and others, I dont care for it AT ALL, looks cheap to me, and I wouldnt do it to a JBL!
As Rob stated, be careful what you do, coatings can add mass, also you might overdamp the speakers cone and change the sound somewhat! Then what? Once you have applied it to the cone, thats it, its on till you recone the speaker!
Weatherproof coatings are used when speakers are used in Direct sunlight, or where there is plenty of moisture, or actual water in the air. If you are on a boat, then it makes sense!
My motto is;
IF IT AINT BROKE, DONT FIX IT!