Some forums I'm on have a range of discounts for paid members, others have access to different parts of the forum for paid members. It's up to the site and companies involved.
On VXRO, there's is a specific section of the forum dedicated to tuners.
This can be a positive and a negative, as it regularly turns into a tuner war, but also, with the VXR being turbo'd, there's alot more options hence they have their own section as there's ALOT of questions.
The tuners are also ONLY allowed to post in that area. Which prevents more tuner wars over the forum.
On AllCorsa, the paid membership give you discounts to some websites and products. But people hardally ever use them, because they arent any use or have expired.
But hey I'm new around here, I'm just sharing some experiences from using forums for around 4years
I personally think that working with tuners works wonders, some tuners go on the sites more than others. Some post up regular offers for forum users. In return the tuner gets lots of respect from members who get discount, resulting in lots of positive feedback for them and alot of people reccomending them