I think it great to ask questions and learn new things. Also for a member to show gratitude for a service or community shows appreciation and sometimes loyalty.
As a new person to this site I see quiet a few posts including one specifically for thank you. Found this post interesting as well because as well as a thank you, it asks a question.
Unless I am wrong, a server, (like any PC that could be made into a server, or router) is limited to bandwidth and online activity as it can only handle so many requests at any given instant however space is relativity not an issue when it comes to text files. As these files are small in comparison say to graphic files which takes up a lot more hard drive space on my computer than documents.
I could type till I was blue in the face and never fill my little hard drive. Therefore I would think that the greatest drain on resources for the server would be the web spaces that users create and not in the forums.
I think the biggest money and the time really revolves around people just using the server online.
However, it looks like the site is interested in expanding and keeping a community. Advertisement and services would be revenue collectors I would suspect.
Sometimes, a positive community is a plus to aim for as well. It has its rewards and can be achieved by providing friendly communication and education which of course involves a little thing called sharing. Please correct me if I am ill informed.