1) I don't think you don't actually have to have an active Premium OM account to still be an affiliate (unless you have special T&Cs) - I was still monthly until after the move, my sub lapsed during the 2 weeks without internet, but my affiliate account was still live and active.
2) the Oddsmatcher it is DEFINITELY an upgrade on the PA one, you have the ability to see underlay and overlay options in the calc screen, a greater number of bookies, more results, more filter options, ability to save filters (I have ones for PP 2UP, Sunbets Half Time for instance), better autorefresh options (if you have the 12 month sub), AND Betfair integration - I definitely like this and the 2% commission is definitely making me use it more.
3) more sign-ups - i.e SuperLenny was one I hadn't seen on PA
4) The tools - The Extra Place Matcher is definitely worth a look (there is also an Each Way Matcher, but I don't use that as much), but also look at Acca Finder - similar to the PA one and I found it found lower QL ones than PA did (the lack of a filter for big matches is a downside though), and the Dutch Matcher - I find it ideal for mugging.