There is a difference between a strong leader and a politically savvy leader. What will determine if Ignatieff is savvy is not whether he votes down the next economic update. His savvy will be determined by his ability to read, manufacture and anticipate public opinion on the stimulus and the Harper Government. If the budget does it's job, Ignatieff would be a fool if he called an election on the economy, whether it's in March, June, or September. If the budget doesn't do what the government promised, then his job will be much easier, as he'll have something to campaign on. However a truer test of Ignatieff's instincts will be what he decides to do if the budget stimulus succeeds, leaving the Conservatives with a one up and the Liberals back to square one. In that case the freshly minted leader would have to come up with a new way to bring about political victory.
You are right when you say , "An election the Liberals cannot afford". For now, they quite literally can't afford it. And indeed, if financing doesn't come through soon, you're absolutely correct in saying that Ignatieff will back down. But if the Liberals can regain their fundraising prowess, possibly helped out by the new web technology donated to them from the Obama campaign, and if the budget measures can be spun enough to show that they have failed, I would say that we would be looking at another October election. But those two conditions are necessary for a 'Liberally induced' confidence vote: significant stimulus failure, and Liberal donor generosity. If those Ignatieff can bring about the latter and be lucky in getting the former, then he would be savvy indeed to send Canada to the polls.