Thanks for discussing!

My specific issue is, I've heard mwi described as saying there is no wave function collapse - all that happens is you, as an observer, end up in a branch that contains a single outcome from all the superposed  possibilities - eg an electron hitting the detector at a certain place after going through alone slit or the other. It is implied that nothing special happens before this, and observation just strips out all the other possibilities ("destroys the worlds").

But the electron at the detector has the properties of a particle not a wave.  If so something must have changed and the only thing that makes sense to me involves some sort of "collapse" from waves that can interfere, to particles that are detected.  Which seems not to be allowed under mwi.

As an aside part of my interest in this is that I feel quantum mechanics may indicate a special role for the observer that puts it outside of the physical world, and can help make sense of many things in our experience that science hasn't been able to inform us on. More on this if you are interested! 

 What you've heard is correct, there is no collapse even in this case what we observe when the electrons hit the wall is one of many possibilities that couldve happened in any of the branches, why an interference pattern is observed doesn't have much to do with interpretations but is due to quantum superpositioning, essentially an interference pattern is a probable "world" in MWI and probable "collapse" in Copenhagen.

To know on why it's probable you'll need to read up on the wave function and superpositioning. It's fun.