I don't know 'MattM', my first 12 footer, Hugh Piggotts design, was a set of lightweight Western Red Cedar blades, each approximately 6lbs, which after nearly 5 years have given me no trouble except a fresh coat of paint every year. But the leading edge some times losses paint and I get a bit of water ingress and that slightly unsettles the balance a bit.
After that all my 12 footers have fiberglass blades, each approximately 9 to 11lbs, with the same design. These were experimental and I am now on some Mk4b's. I now ensure that the internal rib is well joined to the root mounting block, a failure area, and the blade really totally foamed filled. Heck of a job getting each blade back into the mould quick, 6 seconds, and clamped down before the foam distorts the original shape before setting.
Another problem with hollow blades, especially with fiberglass, is water/moisture ingress and balance problems.
If I did blades again they wood definitely be solid wood.
Trouble is, getting good Red Cedar here in Europe is very difficult.