just a quick update Got hold of the 3M kit from eBay and used this on Saturday. Sadly no before/after pics but have to say worked brilliantly. Took a good hour or so and worth taking some time over it but results were as good as new. I'm aware the yellowing will come back in time so will be getting a sealer to slow this down.
If you're umming and arring over doing it, then just do it.
My headlights were going the same way, I bit the bullet & sanded them down using grades of wet & dry starting as I recall from 1200 up to 2500 & then polished with turtle wax safe cut & megs plastic polish.