What about this? Why not only grant a patent if you can prove that you invested a considerable amount of time and/or money to come up with the invention? This protects the often cited expensive research done by pharma companies and puts a stop to all the patents on problems with trivial solutions once you have to deal with the problem. And you still have the first-on-market advantage if you are the first to come up with a trivial idea although you have no patent for it.

Can you think of good examples where this will not work, where we really should grant the patent but coming up with the invention was neither time consuming nor expensive? Of course, proving how much the invention cost you and that it could not have been done with considerably less effort is a non-trivial problem on its own.