I never bothered with it and I don't think I know of anyone who took the Pass Plus course either (I learned to drive at 17 here in the UK, so all my friends were learning at the same time and none of us did the Pass Plus).
As far as I could tell, the only real advantage of taking the Pass Plus was to learn how to drive on a motorway, but my parents could teach me how to do that for free, so I didn't see the point of spending my money on it... especially as I had already spent over £1,000 on learning to drive, all the while being a high school student earning only about £60 per week (about half of it went on driving lessons).
Also, they're supposed to be introducing motorway driving into the main driving test sometime this year anyway, so that won't be an advantage of Pass Plus anymore.
I'm not sure how it affects insurance rates. I don't think my insurance was all that high, but back then (2001) they were allowed to charge lower rates for female drivers (I remember my brothers' insurance a fair bit higher than mine when they got their licences).