I think it would be cool to see a site that shows fluctuations of prices based on time (perhaps quarterly). It would be interesting to see what ponies have gained over time, or stayed static, based on their averages. Are all trending up at the same rate, just because of time? maybe not..
I'm not saying OP should do this.. it just would be cool to see someone do it.
I'm also curious.. the people who do price guides... do they scrape ebay, or do it manually? either way, I can't imagine the work that goes into that.