I have not had the opportunity to read the Court's opinion but am familar with the basic tenet that has changed the ability of non-persons to contribute to campaigns. I agree it would be wise to restrict such contributions and, in addition to a Constitutional Amendment, believe that narrowly tailored legislation would also be useful. For example, Illinois Senator, Dick Durbin, suggests a law that would require shareholder approval for the expenditure of campaign donations. That may be of some use to publicly held corporations (especially if the law required 51% of outstanding stock as opposed to a plurality vote) but is unlikely to address contributions by closely held companies such that a constitutional amendment should be undertaken.

Limits (aggregated by candidate/campaign) across the board would be good. And, particularly if those limits are still within reach of individuals. For example, if we say that a candidate cannot raise more than $100,000 per federal campaign - that should equalize things. Though $100,000 is still harder to raise from individuals, it's still doable. However, if you go up to $200,000 or more, it's corporate territory only, particularly in most U.S. congressional races.

I share your concern (or frustration) and I especially like the idea of a Constitutional Amendment such as you favor.

As much as I like your single issue voter idea, in principle, it strikes me as futile, at best. Any statement that begins with, "If most voters will join me in refusing to vote for any candidate who takes money from donors of kind X, then..." is almost certainly a conterfactual.