I have been a part of this forum before I even owned my first nikon DSLR. This group helped guide in the the right direction and has helped me grow. I would not have known how informative and helpful this forum was if it was not free. If there was a fee from the start, I would have turned the other direction. I am all for a fee (I think $15-25.00 is fair). This site is well worth the money.
New members should be allowed to browse the site on all levels for the first 30-90 days. In that time frame, they can get a good idea of the forum, what the members have to offer and what they can offer in return. I think less than 30 is too short. Some people come here initially to get information about their first DSLR purchase. They may take their time to make this purchase. I think 30-90 days gives them the opportunity to make a purchase, learn their camera/manual and then come here to learn more, ask questions or contribute. Once they have enough experience, they can make the choice to stay by paying a reasonable membership or leave.
As for the tiers, I think this will call for controversy. There have been several times where things have gone the wrong for the littlest things. I do appreciate the labels such as senior member or junior member. It lets you know how long they have been here and how much they contribute. If you add a tier to show how much someone has contributed or paid, it can be a backlash. Some members can throw it in someone else's face such as "well I am a full member blah blah blah" or "Im on the smaller package so I can't afford that or can't afford those services." Though we are all adults, sometimes it is best to not risk the chance of losing members or creating drama over a label.
As for what these different levels of contribution can be, I think offering members different services is good. I love the chat option. There are times where I wish I could chat with someone. I do believe that this will hinder the learning process because some may get comfortable with this feature and not contribute to the overall forum and learning process for all. I think a general rule should be apply that if they believe it will help others now or in the future, to post it in the forum rather than through a chat.
One idea I have for the tiers is for paying members (of all levels or amount of contribution) can have access to certain reasonable things. Moderators or volunteers can create their own tutorials through a video or a written content with photos describing the concepts. They can be different lighting techniques, posing, or how to capture certain things. Each month or more often, they can provide contributors with access to the videos. They can learn from them and make them feel as though their money has been well spent. A different topic can be discussed or shown. In the first week a video is posted and throughout the rest of the month, members show what they learned and post their photos to show their growth from the video. The videos or blogs can be very simple or difficult. I personally would love to watch them. It won't be a competition but a way to interact with one another and learn.
I hope this helps. Though I don't post every single day or week, I am here often reading behind the scenes. Without this forum, I wouldn't be where I am today.