Swords into Ploughshares is a pretty hit-or-miss belief, in my opinion.
At King and below, it might be a pretty good pick if you need the extra food. Bear in mind, if SiP stacks with a lot of food production, you will also need extra happiness than usual, which could be a problem depending on the civ and the strategy you want to go with. Otherwise, unhappiness will hold you back much of the time; think Aztecs with Floating Gardens combined with SiP... you'll grow fast, sure, but the unhappiness will build quickly as well unless you find a mercantile CS or two.
At Emperor and up, it becomes less and less valuable, since almost no matter what you will see DoW's coming quicker and lasting longer from the AI's.
Overall, SiP and Fertility Rites are two nice ways to not have to build Temple of Artemis to pick up a food % bonus, and to be honest, Fertility Rites may be 5% less of a bonus, but it's an unconditional bonus, and given the random nature of what civs appear, what the map looks like, and what the bonus resources will be as you explore and expand, I'd say FR is the better choice.