Essentially using any part of a marketing budget for link strategizing is a waste of time and money.
For the record, I disagree with that.
then just craft web pages worth linking to naturally
I agree with the "craft web pages worth linking to" but not the "just" part. Only a hobbyist can afford the "build it and they will come" mentality. The rest of us have to find ways to be proactive about promotion. In my opinion, link development in one form or another should be a constant, ongoing part of the promotional mix..
how do I convert that in to traffic because that's the only thing my manager will look at. How much traffic -> how many leads - > how much money.
Those are wise questions. The whole point of promotional work is to create new profits, after all. They're hard to answer in advance, though, especially as the payoff from link building efforts might take months to become evident.
What does your company ordinarily do to promote the website, and the business as a whole? How are they measuring productivity for existing promotions? That might provide some clues for how to advocate for the work you'd like to do.
Sometimes the key that unlocks management resistance is "small scale testing". Try coming up with a project you could do as a small scale test and see what happens. If the results are positive, you'll have an easier time getting approval for further work.
When most of your traffic is long tail, here are two places to monitor progress:
"Search sent 22,058 total visits via 4,247 keywords"
"All traffic sources sent 42,955 visits via 461 sources and mediums"
Intelligent link development should lead to growth in all of those numbers.