I'm probably over my head in this, but I think we all aare making serious mistakewhen refering to a mutation. As Gould has pointed out several times there is a large gene pool in any species. So if there is a useful gene (alle?) in this pool there should be many copies there. This could be true even if there is no good reason for it at some time. As long as it is not hazardous the gene will spread out threw the species pool. So if this gene becomes useful there will be many copies in the gene pool to introduce this newfound usefulness.
On the other hand if the only introdunction is a mututation then it is highly unlikely that the gene pool will expand to any useful degree for some time. There could be only one guy in a pool of hundred thousand individuals. The mutation would hardly be of any immediate use.
thanks for listening