Forum earn more than enough money by selling ad slots and any kind of donations are not really needed. They also have huge number of Bitcoins in reserves. If you want just support forum with your money, you can click "Donate" button at the top of the page.
Once I considered wheter I need to buy Copper Membership or no. I decided not to buy it. I know that quite many high ranked members have purchased it without any reason. Maybe they bought just to look a bit exceptionally. But in general, it's worth to buy it just if you are low ranked member who want to bypass some restrictions.