So I think this is mostly true with regards to presidential elections. The reality is that even without SuperPACs presidential candidates are going to have access to millions of dollars. They already did!
Money probably has diminishing returns with regards to advertising -- if nothing else, there is a physical limit to how much advertising you can actually buy. SuperPACs don't get any special rates like political campaigns do, so their money is even less effective, to say nothing of the large chunks that end up going to consultants, third-party firms, etc. I recall a New York Times article talking about how, although Obama was heavily outspent by SuperPACs in 2012, ultimately he was actually (at the time of the article) getting more ad time due to better buying strategies and special rates.
The biggest issue with Citizens United isn't about presidential candidates. It's really about downticket races. House Representatives don't really have very much money to spend on their campaigns, with the consequence that lots of people don't really know who their representative is and almost certainly don't know who the opposition is. Dropping a million dollars on a random district is going to make a huge splash.
So more widespread public funding of downticket races would be a good start (and a good idea anyway). If we want to worry about limiting superPAC spending I would focus much less on protecting the presidential race and much more on fighting organizations that target downticket races.
