Hmm interesting Malcolm;
I've just been reading another astronomy forum (of low repute) and I'm reminded of how easy it is for us humans (myself included, of course), to completely dump an idea and take up another.
Interestingly Science doesn't quite work that way (thank goodness). It would be interesting to see what effects the additional mass might have on the Lambda CDM model. After all, it predicts an absolutely huge amount of dark matter out there.
I think I'm guilty, (to a certain degree), of 'throwing the baby out with the bathwater' on this one.
Also interesting is your question about other stars that might be outside the galaxy.
I had the same thought, but then I wondered what does 'outside the galaxy' really mean ??
Cheers & Rgds