In my opinion you can't easily judge whether a forum is active or not through the hits, you could have daily unique IPs of 1k/day yet their outcome (which is being active, posting, registering etc..) is quite low.
That's why, in my opinion the perfect stat to judge whether your forum is active and healthy is through the stats provided to all users which usually are "Total numer of posts, topics, registered users etc..." because they decide if you're forum is being active and smoothly running.
Another messaure can be used is browsing through the posts made by your users. The value of posts made by users is very important to keep a clean community, and of course to have it a professional one. I've seen a forum where posts contain nothing but "ok" "cool" "really?" etc... In my opinion, those are of zero added value to the general look of the forum. Not that you have to delete them, but their not a suitable mean to meassure. Good ones would be those sticking to a topic, and replying in regards to the same.