Their spending grows commensurately with their fundraising. The cost of maintaining wikipedia is more or less constant. It's a cancerous growth pattern.
The number of articles, languages, and employees are probably not static either.
The number of languages is static. The number of articles is effectively static because 99% are finished and the rate of new articles will be pretty much constant.
The number of employees is obviously going to rise if you choose to spaff more money.