The differences between a "roto-molded" plastic and a hand made fiberglass boat are quite substantial.
Will be much less expensive than a comparable fiber boat.
Will be more durable if put in contact with a hard surface such as a rocky beach or parking lot.
Are easier to repair if damaged, using plastic putty and some adhesive ...
Here is a pretty good article on repairing fiberglass hulls. Its aimed at dinghy's but I guess the same principles apply. Youtube also has many videos on fibreglass repair.
The small leaks should be reasonably easy to fix. Especially if it is just the gelcoat that is damaged rather than a complete hole. The gelcoat is the hard outer waterproof layer which ...
You're definitely right to be looking into repairs for your kayak and I'm afraid, although duct tape may seem a quick solution, when you take to the water you'll want something more resilient! You may find this article on how to make repairs to fibreglass boats of interest.