No doubt some of the marginal money would be wasted, but that's always true and is true now. Science is and would be worth it even if the haircut was immense, and I don't see a reason that the additional spending would be that much more wasted.

Also, the begging scenario you describe isn't particuarly scary. If giving more money to scientists meant there were more scientists each with the same funding levels we have now, that seems like a perfectly fine outcome. If it meant there were more fundraisers seeking money for science and each raised the same quantity of funds, that also seems like a fine outcome.