Well I know that privacy could be an issue, especially when designing a product at Microsoft, but I've often been curious about just who it is that has added my synth to their favourites.
If you look at http://deviantart.com much of the community activity is sparked simply because people can see who has favourited a picture of theirs and usually go thank their fans for the fav. People then reply and conversations ensue.
I don't want to clutter the synth's page with a lot of numbers but I wouldn't mind seeing how many favs, embeds, etc. a synth has, exposed in an expandable stats panel or a section below the related synths list.
As to why it isn't used as much, I wonder if your ratio of favouriters to viewers is really all that different to youtube or flickr users.
As to the feature being too difficult, not at all. A single click isn't an issue. The discoverability question has merit. A text label may be inevitable.