In the title you said F2p but then in the first post you said it was members, so I'll address both.
In F2P, I won't lie - Prayer is probably the best ever amazing thing that you can have. BUT! The fact that it (Prayer) gives you combat levels makes prayer in F2P as a pure very hard to justify. I could see if your skill was able to make up for missing strength levels, but I wouldn't kid yourself. If you fight deep wilderness with high chances of good drops, that extra accuracy could come in help, along with protects, but when you run out you are out, there are no prayer pots in F2P. I would not recommend it.
Ok, for P2P there is a much different story. There are a lot of quests that are beneficial to your pure which also yield prayer expierence, which will generally drop you off at 52 prayer - smite. Doing quests and getting expierence? Baking your cake and eating it too. The simple diversity of all the different types of P2P pures in the wilderness makes it easy for your prayer levels to hold its own on many pures, but unable to step up against some.
Summary: F2P - No, unless you need that extra accuracy and protections when you are deep in the wilderness fighting runies.
P2P: If it applies to your pure (Ex. Dragon Dagger requires a quest, and if you dont do that quest you can't use the dragon dagger, and you can't be a dragon dagger rusher with no dragon dagger)