Jonathan Drori gave an interesting TED talk about the Millenium Seed Bank . The potential for discovering new uses of plants for food, medicine, and construction is obvious, so it also seems obvious to me that we should preserve as many varieties of plant as possible to allow for future uses. As well as those obvious uses there are other potential uses of plants to cope with the changing climate and new diseases. Seeds from salt-tolerant plants have already been sent to Australia to help deal with the salinity problems related to the ongoing process of desertification and excessive use of bore water.
The seeds are stored in bunkers that are designed to withstand nuclear attack, I doubt that such protection will be necessary – or that it would be successful it it was needed.
Jonathan also gave a TED interview with more detail on this topic . One particularly interesting issue is the work on testing seeds for viability and for developing germination protocols to specify the best combination of changes in temperature, moisture, etc to germinate seeds. This research seems to have a lot of potential to improve crop yields.
He mentioned in passing a project to collect folk-tales related to plants which apparently has led to some scientific discoveries.
A related project is the Norwegian Svalbard seed vault which seems mostly aimed at crop seeds . The main difference is that Svalbard provides black-box storage (like a bank safe-deposit vault) while the Millennium Seed Bank owns the seeds. Incidentally the Bill and Melinda Gates Foundation provides significant support to Svalbard (so Bill does do some good things).
One thing that seems strange to me is the fact that governments are prepared to spend such large amounts of money on anti-terrorism but spend so little on seed banks and other projects that can help protect the food supply. If a country such as Australia (which exports a lot of food) was suddenly unable to produce enough food to even support the local population then the consequences would be much worse than anything Osama could dream up.