For me buying the Forum Software is ok, but I wouldn`t want to pay for single Plugins.
But you want to use those plugins. I don't blame you. Actually this is the well known saying for plugins at all (any forum, any framework). Similar to "I'm willing to buy the house but I wouldn't want to pay for furnitures".
Really can't understand the reason. Do you think that to code a plugin or design a style, is a few hours work? Believe that some plugins that you'll find here (same in other forums, same for Wordpress, same for Joomla etc), maybe are some months work. Coding for a framework is much more difficult that coding single PHP scripts because you need to read/understand and follow some special coding rules. The same applies for designing a style comparing with simple HTML templates.
As I said before. I don't blame you. I'm blaming the "defacto" that exists for plugins.
And yes, especially for vB4 you'll find a plethora of well coded plugins and styles.