The thing about PvP gear is that it doesn't have the Mp5 for long sustained fights. You'll have a good amount of crit, which is nice, but you don't want to completely focus on that. As has been mentioned in these forums many times over, a balance of Mp5 and crit rating is essential for maximum efficiency and longevity of heals in terms of gear selection.
It's ideal to just spend some time and yeah, run the instances again and again until you get the piece (or pieces) that you want and move on. If you have a good raiding guild they can help you do this, or if they ar good enough and want to, they can carry you through kara and you can gear up in there. It's also nice to gear up in the instances so you can get your reputation up and get some nice faction rewards along the way.
It's really not as bad as it sounds, and not only can you pick up holy gear by running the instance, but you can grab some prot and ret gear too if you want to try tanking it up or do a ret weekend for some fun.