If memory serves, Huffington spent gads like this and got trounced. Plus, Brown has the media (except FoxNews), which is worth quite a lot to Dems. Whitman may well be spending her own money though. If she wins there will be no shortage of people looking to contribute to her "campaign" to buy favor. If she loses, who is going to want to contribute to a lost campaign?
In my opinion though, no campaign contributions should be allowed after the campaign is over, as this basically allows candidates to sell influence after the fact. If you want to loan yourself millions for your campaign and it isn't made up by others during the election, then you've spent your money and any money received after the election should be considered as income and taxed accordingly.