As far as handling the data, I use MS access which should handle that many entries. If there's only 131,593 active caches, that shouldn't be a very big file, so downloading weekly could be a posibility. As far a providing a list of 500 waypoints to be downloaded into a GPX file, I would think that this would use less processor time to compile.
I posted these as ideas to Jeremy to think about. When I was doing Y2K programming on Main Frame computers I had to move a lot of data in different ways, and across multiple platforms. As I work on creating solutions I will offer them to Jeremy for use on his servers.