Perch is a good makeshift fullback. Raylor is definitely not. Raylor is a great midfield player and has some good qualities, but he can only play fullback if he's basically got Jonas right in front.
I think you're right that Simpson gets unnecessary stick, but I don't know how you can say Raylor can't fill in at full back after his performances this season, he was brilliant and only displaced due to injury. Plus, with him, Cabaye and Ba on the pitch together, we have 3 very good (if very different) set play specialists. That can't be ignored, just like you can't ignore Simpson's ability on the line!
As for the Reading link, I think they're going about things the right way to be honest. Guthrie on a free, Simpson for a couple of million - they're both steady players who are reasonably young, have plenty of Premier League experience but still have a lot to prove.