Of course, PageRank leakage is nothing to worry about. And indeed ranking might be improved by adding additional link to a page due to the benefit from on-page optimisation. Nevertheless, the leakage effect exits.
The effect of adding a new page is increasing the (real) PageRank of (almost) one (strictly spoken it depends on the linking structure). In case that that you're having a page without outgoing link the effect is much better. However, while the effect of adding a new page for the original algorithm can be calculated one has to say that Google changed the algorithm significally some year ago. Have you ever tried to add billions on pages and 'produces' PageRank? It won't work. Instead of 'producing' PageRank you nowadays need PageRank to get the pages spidered.