I agree. Indeed, it's a very good question whether Wikipedia shouldn't just operate.
However, as I said in the other comment I made, this growth seems to be needed in order to maintain, "just operate", the achieved purpose of Wikipedia - online, open encyclopedia. The growth is needed because online, open encyclopedia is itself a moving target. The main problem, it seems (as pointed in the Annual Plan[1]), is the trend of fewer contributors with each year. If you read the comments at theregister article, all of them talk about the bad experience of editing a wiki and engaging with the contributor community. Now, I have no idea how true this is and how often this happens but the fact that there are fewer contributors each year remains. Wiki edits and the contributor community are the lifeblood of Wikipedia. If these and their quality are waning, then this will have a large impact on Wikipedia being an encyclopedia. Furthermore, to be a true encyclopedia, the quality of the articles needs to be as accurate as possible which certainly is a moving target. Investing into additional tools to better assess articles' quality certainly works towards this target.
Next, there is open and online. Part of the money goes towards broadening the reach of Wikipedia. Like making it available in the Global South via mobile for free, with no data charges (Wikipedia Zero). Or consider lobbying - if the foundation itself does not defend itself from acts like SOPA and thus remain online, who else should step in to WMF's interest? I think it's fair and very empowering to have people with very limited Internet access to at least Wikipedia.
With that said, the question changes. It is not about whether Wikipedia needs more money - it does - but it is about how much it needs, i.e is the foundation efficient enough while maintaining the target of an online open encyclopedia. revelation's comment[2] about hiring as a startup is quite a interesting comparison
[1]http://upload.wikimedia.org/wikipedia/foundation/4/4f/2012-1...
[2]https://news.ycombinator.com/item?id=4947473