Ok, here is my summary: What makes a bbPress forum better in eyes of search engine?
- proper use of headings
- more semantic HTML, no layout-tables
- pretty permalinks
- trackbacks (sending or receiving or both? how do they help?)

Is there something more? And is there any evidence about the impact of points 2, 3, 4 on page rating?

Don't get me wrong, just trying to have clear knowledge. I'm a user of bbPress too and like it, but I have doubts about being it a significantly better platform for SE.