The problem with 3rd party plugins is not the money, it's the process.
It's the inconvenience of having to install and maintain them. It's the perceived risk involved. You have to buy them through random websites and companies that you have little or no relationship with. What's quality control and security like? Is their plugin popular enough that it will make enough money for them and still be around next year? What do we do if we centre our workflow on a plugin and then it stops being developed?
Money is a factor but I would suggest it's the least of people's concerns.
What Vectorworks needs, preferably within the application itself, is a marketplace for third party plugins that let's you browse and search for plugins, rate them, review them and download them. It would manage installation and updates automatically and would offer some sort of quality control and security.