Einstein@home really goes at great lengths to reward their crunchers. They carefully monitor their whole process to single out those workunits which yielded a discovery (not always an easy task in computational science when you handle loads of data). Then you get an e-mail from their top-scientist, Prof. Bruce Allen. Then you receive a framed discovery certificate with a personal letter of appreciation from the same. Then they publish their findings in the Astrophysical Journal (a very prestigious scientific publication) where they mention you as one of the volunteers who made the discovery possible.
Other BOINC projects are making a big mistake in not implementing some of those perks. I know that it's not always possible to single out "the discovery workunit" but I am sure they could do better than providing no perks at all. The cost of such things is really minuscule, and their marketing potential (so to speak) is huge, probably larger than any reward you can realistically get with Gridcoin or any other crypto.
Good points. Volunteer crunchers need more feedback, an opportunity to taste discoveries. It is very important, as without positive feedback people easily burn out.