RAID does a few things: Gives a storage system higher reliability, higher speed, and higher capacity. Depending on what RAID setup you use you can have one, two, or all three of those things. As such the question is what are you wanting from your storage system?
As to SSDs in a RAID the main thing is right now there are no ways to implement, or at least no ways that I'm aware of, Trim once you do that. Now some people have done it regardless and say it works fine for them. I personally side with having Trim active.