The 17 is a lot more maintenance due to fiberglass and gel coat.
This is just a propaganda generated by plastic boat owners to make them feel better about their boats.
But, seriously -- fiberglass requires very little maintenance. Once a year, you may need to do a few touch-ups with some gel-coat. If neglected, a boat may need a "bottom-job". There are pros and cons for both. Fiberglass is roughly10x stronger and stiffer than a polyethylene. This is makes fiberglass boats lighter and generally allow better sailing performance. What is perceived to be maintenance-free about rotomolded boats is what happens when a hull meets a rock. Because fiberglass is so stiff, the material does not deflect and stress concentrates on very small area. This results with a scratch or worst a crack. With more flexible polyethylene, the stress get spread out and there is no damage.
On the other hand, fiberglass is very repairable. All can be fixed. On occasions, with a big damage to a hull, it is just better to replace the hull, because of the amount of work required. With polyethylene, a home-repair is pretty much impossible. There are some methods to sort-of patch-up small damage. If your hull gets a big hole or a crack, it is done. To be fair, you would have to try hard to make this type of damage. You can't repair scratches or repaint a plastic boat.
We also know, there are 50 year-old fiberglass cats still sailing. With polyethylene, this is still to be determined. In principle, all polymers would sustainable some UV damage over years. UV acts as a catalyst for polymerization process, resulting with the material to become hard ad brittle. However, if a boat is stored covered, I don't see why a rotomolded boat would not last for many decades. I would be careful in getting a used boat from a resort. They typically are stored uncovered on a beach, year around.
Both materials have pros and cons. It all depends on your needs/wants.