I really liked that Ash's consciousness was in it, although I was disappointed he didn't play a more active role in the story.
To me, the Ripley mind-wipe thing was just a cheesy get-out clause. As you say, there are other times when it could've been used in the series (Aliens, Alien Resurrection; "Why does it have memories?!") and the fact it was never even suggested makes its use on some run-down mining vessel operating in the arse-end of nowhere seem even more convenient and dubious.