I am not sure about Peace Corps, but I participated in AmeriCorps for two years and am quite certain that it made a difference in my application. Although some interviewers were not familiar with the program, many found it interesting and were quite curious about my experience. The program I worked with allowed me to reach outside of myself and the learn about the struggles in my community. Since I worked with an epidemic that many fear (HIV/AIDS), interviewers were especially interested in how information was presented to say - someone homeless versus a corporate type....and in one case the ethics of it all.
There are a few bonuses to AmeriCorps: the contract is one year in length and at the end of the program one receives an educational award to apply towards tuition or pay back student loans. The 'stipend' during the program is not much, but the experience can be amazing.
Some food for thought.....good luck with the decision.