If i remember right when you raid ssd's you lose trim support (if supported bt your ssd) so u have to defrag regular to keep performance but this may not be entirely correct. More research i think.
With regards to the speed difference their is an obvious reduction in boot times, load times etc but to upgrade from what you have may be expensive. Based on 2 mushkin callisto 60gb ssd at £90 each from aria (there are cheaper but slower and less support ones) thats gunna be £180 without a raid card (if thats what you run?) I believe that you would get noticable speed increase but with the high price and setup its a personal rather than cumpulsary upgrade