Well i have ran many forums in the past and in my experience vbulletin is a much better forum based software then phpbb. Functionality wise and customization abilities along with a more user friendly CP. Has it ever been discussed using vbulletin?
VB costs money; phpBB is free. ILP doesn’t turn a profit, so a cosmetic upgrade isn’t a great justification for the switch.
It isn’t just a cosmetic upgrade, all around its better the phpbb, but it was just a thought. Do a donation drive if 200 people donate a dollar you got your vb liscense right there. You can then just convert your phpbb database to VB
Sure vb is a lot better (and takes more time to set up, too).
If you donate vb license fee for next 5 years to ILP, I guess it may happen. 
Also, there are lots of plug-n/modules for phpBB.
If you want specific feature, there might be an easy way to achieve it.
(But we’ve got be careful about these modules because some of them aren’t very well written and it may increase the risk of cracking, etc)
I’d say stick with phBB, almost all forum goers are familiar with it, and its fairly easy to learn if they don’t. It has a simple straight to the point layout, and is easy to naviagate.
Its sort of like the Linux or Windows argument, Windows maybe a lot better, but Linux is free. Nothing beats that (at least in my anticapitalist point of view 
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