Throwing things at the wall to see what sticks is precisely how drugs were developed before the 1970s. It's called phenotypic screening, and it worked quite well. There's an argument to be made (Derek Lowe makes it here [0]) that it worked better than the modern method of target-based drug discovery.

[0] http://blogs.sciencemag.org/pipeline/archives/2012/04/16/phe...