I remember reading that the Tories were the only party with any money in the aftermath of the the 2010 General Election as Labour were basically bankrupt with big debts and the Lib Dems had spent their warchest. The Tories in contrast were relatively debt free, still had some money in the bank and had lots of rich donors to call upon.
While UK elections are a lot less money dependent than US one's money is always helpful so the financial factor alone might win the them another few seats.
Oh Tories had financial problems, but were far more prepared for a national campaign compared to their opposition.
You also have to take into account that initial budget and what Osborne does with it and the potential gains or losses. Initially the 2010 budget resulted in a increase in the polls for the Conservatives but that could have been based on the honeymoon period for government and the budget in this scenario would be different.
Without the coalition, we also have to consider just who else comes on board in his cabinet to keep his backbenchers appeased. So, lets say a 4th November election he also has to content with Nick Clegg not losing popularity among his supporters and if he is able to play it smart could take support from both Labour and Conservatives.
The leader of Labour is another problem, that election will be done by September most likely. They know there will be an election within 12 months so will likely choose someone they think will win so David probably wins.