I think this answer always depends on how many games you currently have - and what type of games less importantly. Also if you want to back up your games.
If you have 30GB of games then what's the point in getting two 250GB (+) drives in RAID.
Just don't see the point myself. Sure it saves money, but it more than often gives more space you won't use and if you do use it, you'll need to back it up cause it's in RAID (talking 0 here) anyway.
If you can stand the noise, a raptor in a system is always a nice thing to have, imo.