State funding of political parties creates far too many difficulties for good governance to be a good idea. Such a move would leave the funding of political parties dependent upon the government and, therefore, create powerful electoral incentives for the government to change the system to skew it towards advantaging their own side. While it might lead to fewer funding scandals they would be replaced by massive cynicism each time a government attempted to fine tune the funding formula and commentators saw unsavoury motivations behind the changes. These fears won't always be irrational, the recent problems with Labour pushing postal voting too fast and risking fraud in defiance of the Electoral Commission in order to shore up its Northern vote provide an important example of the sort of trouble we don't want to see in the funding process.
Caps, as supported by ConservativeHome, are just as problematic. Last time these were floated it was a Labour response to Lord Ashcroft's financing of the Conservative party, the new Conservative enthusiasm for them can be traced to the widening of the Conservative funding base following the election of David Cameron. The level of the cap provides the ability for governments to adjust the system in their favour and, therefore, creates the problems described above for state funding.
The solution to this crisis has to be more along the lines of the ad hoc Labour response. When there are crises due to poor information in industries like financial services the best regulatory response is not to restrict the risk or return of products (a cap) or to have the state step in and nationalise (state funding). A proper role for government in situations like this is for it to ensure regular accounting standards and open information. This is a crisis caused by a lack of open information; the proper response is to let the information flow and leave the judgement on whether a party's funding is proper to the electorate.