Definitely. But it depends on whether you're min/maxing 100% or not. I used to do that, but I got in so many arguments with other priest about it because 19sp =/= 23sp. This was particularly problematic when I was apping to other guilds and would get into arguments with the guild's token priest. Everyone has their own right way, you know? It would always be socket bonuses vs. no socket bonuses, crit vs. straight sp, divine fury vs. spellwarding, int meta vs mana return meta. (Once it was even haste vs. crit, during a month long haste kick I was on... I try to forget about that.) Going straight SP just became the easiest choice because it was supported by the priest community at large (even if there are plenty of progression priests who defy it) and thus one less thing to argue about on my apps.

As for Penance, it depends. It's the first spell I go to when I spot heal a target, and crit helps, but since I started raid healing more, my targets are a lot more random so crits and DAs are usually overkill. In my last guild I actually went easy on backing up the tank on most fights, because the main healadin was so on top of the healing, and he had a really top notch shaman to back him up. You feel pretty useless as a bubble spammer sometime so healing a tank for the sake of applying a DA isn't particular gratifying when combined with the existing role of applying shields. To make myself useful, I often opted to help out in reducing our time spot healing the raid, by picking out the least likely to be healed targets, and healing them first. That way I worked backwards in "priority" and met other healers in the middle. It always seemed more efficient that way, and made me feel like I wasn't overhealing much. This is the funny thing about progression raiding healing - it actually a lot less fun on an everyday basis because everyone is so good at their jobs. You never have any slack to pick up unless something unexpected happens, so the only time when healing is fun is when stuff is new and unfamiliar.