Scenario: A major ecological disaster occurred five hundred years ago, in which large numbers of species (including almost all wild fauna) went extinct. Assume that the environment both before and after is modern-Earth equivalent; effects not discussed here mitigated the major effects on temperature, environmental composition, etc. Humans survived, although not in vast numbers, and in doing so preserved a number of highly productive and easy to grow crops along with some domesticated animal species. A few clever biologists also managed to preserve some really ecological critical wild species, like some relatively flexible pollinators. However, all of the non-human populations suffered some fairly extreme bottlenecks, in some cases probably down to the equivalent of a couple of seed packets. Humans only had a couple of months of warning to prepare, and not all species would have been preserved by people with a strong understanding of either theoretical or practical genetics (e.g. animal breeding). Unlike most of the other genetic bottleneck scenarios I've seen here, this one explicitly does not have a maximally diverse population during the bottleneck, which presumably would make the effects worse.
Five hundred years later, what kinds of problem (if any) is that lack of diversity going to cause, and how valuable would it be to have someone show up with new viable samples from the original populations? Does having a hundred new samples make a meaningful difference over just one? It will presumably vary by species, but I don't know what factors would make a difference one way or another.
With regard to what "valuable" means: I'm trying to figure out how excited a biologist who works in species maintenance and restoration would be to find these new samples. I am, unfortunately, not enough of a biologist to even guess at the correct criteria to use to evaluate this question. I'll happily revise the question if someone has suggestions for more precise criteria.
We can assume that the humans have been doing responsible husbandry for all of the domesticated species since the disaster, and that they started doing at least some preservation efforts for the wild species several decades after the disaster. A few species would probably have been lost to disease along the way due to common vulnerability; would we still be worrying about that, five hundred years on?