Move the "XenForo Bug Reports" to a support category. Do non-customers really need the ability to view or make bug reports? I can imagine a non-admin user of a XenForo site wishing to report a bug, but such users should probably ask their site admin to bring the matter to XenForo's attention. And any bugs noticed by potential customers whilst demoing the software could be reported via the Pre-Sales forum.
Make the support forums invisible to users who lack a customer account. Since these forums are resources intended to support paying XenForo customers, they need not be visible to anyone who hasn't paid for the software. Removing them from the public eye will clarify this distinction.
Beef up the public forums to give potential customers the info they need. Making the support forums private would deprive potential customers of information they need to make an informed purchase decision. This can be remedied by augmenting the public forums. For example, a "XenPlus Showcase" forum would give third-party developers a place to repost or excerpt information publicizing their add-ons, styles, and language packs. (Such a forum could be writable by customers but viewable by all.) And perhaps some of the information in "Tips, Tricks, and Guides" could be moved to a public forum, as prospective customers will want to see guides and tutorials for basic operations before deciding to buy.
Enable even visitors to click and enlarge thumbnails in the public forums. Prospective customers want to know how XenForo works, what sorts of add-ons and styles are available, and so on. Looking at screenshots is often the best way to get that information. Forcing people to register in the forums to get this information can deter interest in XenForo and put a damper on sales. Anything published in the public forums should be fully available to the public (though this means more attention must be given to the appropriateness of information posted in these forums).
... This last point was something that particularly irritated me when I was trying to decide if I was even interested in considering XenForo. I hate it when forums force me to register just to get the information that I need in order to decide whether I want to register.
The above list may not be exhaustive, and I certainly won't insist that any of them are necessary. They're just a few thoughts off the top of my head that I respectfully present for your consideration and discussion.
My apologies in advance to the mod staff if this results in an increased workload.