I am a moderately experienced kayaker and have used both plastic and fiberglass kayaks in the ocean and plastic kayaks in whitewater. I recently had my ocean kayak stolen, so I’m back in the market for one. The old kayak was plastic (cheaper) but I am open to paying the extra money for a fiberglass kayak. However, I am not sure that I see the value of double the cost. I have always been told that fiberglass kayaks are lighter and looking at the weights of similar kayaks, thatis true but not by much - e.g., 60 vs. 53 lbs. Plastic kayaks are more forgiving with being dropped and hitting rocks but scratch easier - true? But it would seem to take a long time to dig a scratch copmpletely through a kayak - at least, with my level of use. Fiberglass kayaks are more scratch resistant and, being stiffer, will be more efficient to paddle - true? But how noticeable is it and is it worth twice the price? What is the advice of more experienced paddlers?
Boredom factor - if you have a plastic kayak, you may be more likely to keep it for a few years and then sell it to someone else and get something different - the latest and greatest design. A fibreglass boat you’re more likely to keep for the long haul.
I’m still a beginner but I’ve already bought and sold a number of boats. On the used market I’ve found older composite boats can often be had for not much more than newer plastic ones. In fact I purchased a used composite boat for the same as I paid for our other plastic boat. I would buy either, the hard thing for me has been finding low volume ones. The plastic boat weighs about 7-8 lbs more, which is very significant to me when car-topping. The composite one also feels a bit nicer on the water, but not super noticeable for me at my stage.
Tooling for composite kayaks (and canoes) can be less expensive that that needed for plastic ones. This allows more experimentation in hull design and also finer lines. The older layups, especially Brit boats tended to be quite heavy. Some of the newer ones if you can stand the price get the weight down while retaining strength. That said, it looks like weights for some of the RM boats like the P&H Corelite X hulls are getting better. My new Delphin is listed at 55 lbs & seems to be close.
Digging further into the differences in regards to repairability.
As you said, plastic gets scratches somewhat easily, but it takes a lot to scratch all the way through. Or otherwise punch a hole in one. They are rugged. But once you do scrape a hole in one or punch a hole in one, they are difficult to repair well. Plastic welds are much weaker than the original plastic. And if the boat is older, the aged plastic is even harder to weld.
Composite boats often feel more fragile (though most aren’t, unless they are a very light layup). But if you do damage a composite kayak, the kayak can be easily repaired, even on expeditions. This makes them the material of choice for most long expeditions.
I have plastic, fiberglass, and kevlar boats. If crashing into rocks is in your future, then there is a good argument to be made for plastic. If you want to lend the boat to friends, plastic might be good. If you want to put your kids in the boat, again with plastic.
If the above do not apply, there is no argument to be made for a plastic touring boat. Plastic boats are heavier, they have leakier hatches, their bulkheads are not as watertight, and their hulls fuzz up over time and develop dents. The weight differential alone will mean that you will paddle it less.
Do what was recommended above: shop used composite boats.
Plastic has its places, well listed by Acadia.
The models I want tend to be mostly available composite. Plus plastic hatch covers have a much bigger tendency to leak than those on a composite kayak in my experience. You can always put on a keel strip, and gel coat is pretty easy to replace if you need to.
Fiberglass canoes and kayaks are stiffer and as you said a little lighter than plastic. I love the stiffness. I hate to see the flex in the hull with each forward stroke in a plastic boat. That flex is wasted energy. Also a 10 lb difference means a lot when the boat gets in an awkward carrying position such as removing the boat from a cartop and a sudden breeze hits you. Then your back may wish the boat was lighter.
If you’re not doing whitewater then rocks shouldn’t be a problem. Anyway scratches show you’re paddling and not just storing the boat in your backyard.
I wanted to find a lighter kayak. My 20 year old plastic Necky Kayook weighs 63 lbs. at 15’ 3". It’s still a great boat, but putting it on the truck in the wind kept getting harder. I bought a slightly used Eddyline Journey, made of carbonlite (still a plastic) weighs only 49 lbs. at 15’6". It’s been a terrific boat, and the weight difference really makes transporting easier.