I think its probably closer to 90% just going by how many posts have paid signatures underneath them. In theory sig campaigns should just be a bonus to people who were already posting anyway, and I think for some posters this still holds true. However, its pretty clear the vast majority are here just for the payday. This has led to an ingrained culture of shitposting-for-cash where genuine contribution is quickly buried beneath a flurry of dull, meaningless drivel. Most visitors who aren't already a member here aren't gonna wade through it to find the rare, interesting nuggets of information... they've effectively stopped coming here.
I just counted, and in all signature campaigns, paid in bitcoin around 415 members participate. I did not count the Stake campaign because I can't find the participants list and 1xbit for obvious reasons. Plus other campaigns where payment is in tokens, I believe there are about 1000 members in total who are paid for their activity here.
maybe Loycev or someone who deals with statistics can provide information on how many regularly active accounts there are out of 3.5 million registered while "only" 1000 paid for that.
in the end, several other forums tried paid to post and none of them survived.