I agree Bruce. Removing teak can affect the resale value of some boats, Grand Banks being one of them because to most buyers, teak decks are a big part of the aesthetic appeal of a GB. On the other hand, a teak deck that is failing or worse, causing problems with the subdeck, will devalue a boat a lot more than replacing the teak with fiberglass.
However...... the fiberglass job needs to be really top notch. I've mentioned in the past the re-decking job the owner of an Island Gypsy on our dock did a few years ago....
The project took him a summer and a half, and the end result looks better than the manufacturer would have done at the outset... Absolutely beautiful job, and I think it added a lot to the value of the boat.
He did the whole main deck. So there is no teak decking at all on the boat unless there is some on the flying bridge. I think no teak at all is a big plus to a lot of buyers these days so I think he did the right thing.
I think some teak and some glass can look very good depending on the design of the boat and how well the break between the glass and the teak is done.