Your suggestion that there be a "limit to the number of backers on a project" would have probably saved the elevation dock guys some grief. On the other hand, I want the Planetary Annihilation guys (Digital Product) to have HUGE oversubscription - we got funding for Metal Worlds, Water Worlds, Galactic War, and an Orchestra Score through extra funding!
They could easily set up a bullpen of 5 projects to soak up extra funding. It is completely pointless to fund a project over its budget. The project can change its budget and plan/promise of they want to raise more.