A fibreglass kayak of that vintage (30 plus years) would definitely be polyester/'glass and I'm thinking possibly built using the chopper-gun technique where fibreglass strands and resin are blown or sprayed-up into female moulds after a previously applied gel coat. This results in a 'sturdy' and weighty craft where strength is relative to the thickness of the lay-up and dimensions of the boat.

Wear and sunlight would be my concerns as 30 years exposure to the elements as some of these boats seem to endure can really chew up a gel coat (the outer pigment-infused layer of polyester resin).

I'd repair only the damaged areas requiring attention using polyester resin and cloth as needed, feathering these areas well back from the damage, repairing slightly proud of the original surface, and fairing back down using successively finer-grit paper as you go. Repair either side of these faults if at all possible.

Forget applying a layer of glass over the entire hull. It's probably heavy enough already, and this likely won't add any significant structural strength or rigidity.

If the gel coat is seriously compromised, ie: cracked, crazed and oxidized, I'd suggest that re-applying a new gel coat. As with painting, you'll still need to remove the old layer(s) mechanically, and have a smooth layer for painting. After painting on the new gel coat by your favourite method (an even layer is desireable), you'll need to wet-sand and buff out the gel coat after it cures.

A little more work, granted, but a more durable and pretty result.

Mark