I have been in xenforo resources. I can tell that it really works.
Developers start to flooding the resources with add on to create sales and competition will down the price and create better quality add on. Don't worry about free add ons it is alive too. You can see no price tag that is free one.
2000 add ons you cannot never denied the success of stimulating add ons.
https://xenforo.com/community/resources/
The idea to stimulate by allowing premium section is good. But the resources add on by xenforo itself is a killer.
Indirectly you stimulate vb5 sales when new buyer deciding it take a look at this market too.