I'll try to get us back on topic...
Here is the ideal...
Regardless of WHATEVER popular Forum software you WERE using. You would like to START to run a UBB™.
Since you don't want to start your community from scratch, and lose all of the topics and posts that your members made, you need a conversion tool, so that all the old stuff can be migrated to the new board.
Rather than having a tool to import *just* vB threads, you would be better served to have a tool to convert from most popular forums, including vB, Ikon, etc.
A lot of people would probably like to switch to a UBB™, but may be hesitant to do so for fear of losing old threads. Therefore a flexible tool would better serve both IP and those wishing to do so.
That's my $0.02
-Tacks