No. PageRank has gotten more, more, and more irrelevant to getting good SERPs. Google takes into much more than that.
The forum I owned before I sold it had a PageRank of 0 (updated on April, never updated since) and it was easily able to shake up the SERPs of RockBand.com and ScoreHero when...
If MyBB gets Facebook Connect and Twitter Connect, then it will win for sure. Nonetheless its simplistic Admin CP IPB 3 is also a good choice. It's got excellent SEO out of the box along with Facebook/Twitter Connect as well.
I kind of find phpBB is not modern enough - it lacks AJAX features...
You can't. You might be able to live without gizmos and gadgets but you'll always have technology in life (I mean, stuff like carpenter tools and stuff also count, don't they?)