what happened to the Heritage Fund anyway?

Short answer:
The Progressive "Conservative" govt blew it, and is blowing it, on consumption. And I'm not the only one to have issues with the spending spree:

[Albertans] want a government that's going to deal with the basics instead of of spending, spending, spending
- Alberta Liberal leader, 24 Jan 2008

... with all the spending they've been doing, I don't think the budget is going to be pretty.
- NDP MLA, 24 Jan 2008

When even the Liberals and the NDP are raising their eyebrows at the spending, one wonders how long our P"C" supporters can remain in denial about their party's addiction to big government.

But even if the government contributions were anemic, wouldn't the fund's natural growth have made it larger than it is?

Sadly, not only were contributions anemic, but your Progressive "Conservative" govt added insult to injury by frequently raiding our long term nest egg to fund current spending.

Which brings us to the Wildrose Alliance's platform:

A Wildrose Alliance Government will limit withdrawals from the Heritage Savings and Trust Fund for government purposes by requiring authorization via a binding referendum on all such withdrawals.

A Wildrose Alliance Government will institute a policy of depositing a set percentage of government natural resource income each year into the Heritage Savings and Trust Fund.

A Wildrose Alliance Government will build up the value of the Heritage Savings and Trust Fund with the goal of using a portion of the interest earned by the fund to eliminate Alberta personal income taxes.