We get a request for collection value to be implemented on a weekly basis. As of now, it is not something VGCollect is interested in doing. It is simply unreliable as every single day, the so-called value of each item will fluctuate and make it a full time job just to try to keep this up.
If you are interested in the value of your own collection, you can visit Ebay/Amazon/whatever other site and just look up each item's selling point. By the time you are done, the value will have changed though so it really doesnt matter anyhow.