Horrible idea solely because of the expense and the flood of cash it would put into the political system.
There is already a flood of cash in the political system. But it's dominated by the less than 0.5% of Americans who ever make a campaign contribution that is large enough to be publicly reported (greater than $200).
SCOTUS has more or less said we can't restrict that flood of cash. If that is the case, I don't see an option other than making sure the flood isn't only coming from a few very large spigots that exercise disproportionate influence as a result.
A constitutional amendment more or less stating that monetary donations are not protected speech would be DOA precisely because the sort of people who already donate millions of dollars to their pet causes would donate millions of dollars to preventing that from happening.
If politicians can get a larger share of their campaign funds from people who are only giving them a few hundred dollars - and who will not and should not expect any "favors" in return - they can rely less on the sort of people who give more and
do expect something in return.
The fact that two very wealthy men (Sheldon Adelson and Foster Friess) were able to needlessly prolong the 2012 Republican primary by several weeks despite their respective candidates having nowhere near the support needed for a plausible path to victory tells you something is very wrong with the way we elect people.
The fact that the 2016 presidential election has more or less already begun and spending on it will stretch into the 10+ figures when the rest of the developed, democratic world can elect leaders in a couple of months at a fraction of the cost should tell you we are doing something wrong.