I have several lightweight composite canoes and kayaks (fg-kevlar,
carbon-kevlar) and also three Royalex canoes. Don't specifically know
anything about spectra.

If money is not an issue, I would always go with the lightest material.
The only circumstance I would get Royalex is for a boat that will be
used for heavy duty whitewater ... where you are likely to dump and
wrap the boat.

Kevlar composites are very abrasion and impact resistant ... and they
are easily repaired. Royalex will flex and slide over submerged rocks
better ... and it can "pop back" into reasonable shape in wrap and pin
situations that might break a composite boat in half. Usually that
happens when you are out of control ... or out of your boat ... in
whitewater that is too difficult for your skill level. When seriously
damaged, Royalex is essentially unrepairable ... though you might find
a welder who can do some repairs.

Lightweight Royalex will lose some of the strength of full Royalex and
the hull will probably have noticeable flex. If not at first, then
later. Royalex hulls will "oilcan" as the years go by, and light
Royalex would be more susceptible to that. A well made composite will
stay rigid for its life if well-maintained and if damage is repaired.

For fla****er, swif****er and easy whitewater (if within your skill
level), I would go with a lightweight composite. Composite boats have
finer lines and edges, can be accelerated quicker and can be paddled
faster. Light weight is a blessing when carrying the canoe, taking it
on and off a vehicle, expecially as you get older.

The Propector is a beautiful canoe. I wish I had one. That was Bill
Mason's boat. His was wood and canvas. He said in Path of the Paddle
that his ideal boat would be a kevlar Prospector. He said that at a
time when Royalex had been around for many years.

I'd look into Novacraft's "blue steel" layup, which seems to be
kevlar/carbon and is even lighter than kevlar/spectra.