The question is how will we track and measure how much value a funded project is provided?

There are blockchain history elements generated for all payouts, just as there are for content payouts today. UIs like the many we have for existing Steem functions will process this history show the data. We know who are the largest earners on author payouts, curation, who is powering up and powering down, etc. because of the many UIs and reports that have been created by the community to show this kind of data.

The initial version includes a pretty limited web UI that shows proposals and allows for voting on them but I have no doubt that over time many additional UIs will be created to show the data in more and different ways (some may even have their funding provided by SPS, some may not)