Great post Mike!
I agree and keep all your advice in your post above, just some things need to be clarified
7. Keep the forum up to date and stay on top of the subject categories as they grow in popularity. This may mean that the first year you are adding and deleting categories as you find what your users are most interested in.
Do this you can make more broken links after you removed links of categories, for any URL structure of some forums, it also could affect URL of threads, which is harmful for your search rankings.
Are you do a research forum names (or its popularity) before putting them on your forum? If no, we can face problems as said above.
I also agree with you that removing or adding forums depends on activities of users are really wise ideas and I did on forums
8. Listen to your members and be responsive to what they are looking for. They can actually help you achieve number 6 if you are not to hard headed to listen.
But how if some members recommend or suggested you wrong ideas so it can affect your forum if you change according to their ideas.
For example: some people on other forums said that this forum theme is complex and not good for them and suggested me change to traditional layouts of forums
while some liked it or even I had dozens of emails asked to buy this theme ( mean they thought it was good for them and they wanted to buy). so if you are me, you will change template or keeping it as current one? what will change your decision?
9. Stay on top of Spam - this is a constant battle on a good forum. The more popular you become the more you will become a target of hijacking and spam.
You are exact about this, spams on forums are really a big problem for all forums, happen on all good forum CMS's. Do you have any experience on stopping spammers and spam posts? Would you share some in details?