Having recently lost a beautiful, 2 yr. old tuxedo to FeLV, I quickly had his mother and brother tested, fearing the worst, and they fortunately tested negative. I then had them vaccinated. All three stayed primarily in our backyard and were in and out during the course of the day. We do not have a concentration of cats in the neighborhood, as we are spaced pretty far apart and are in a wooded area. Due to the contagious nature of the disease, I can only guess that Gateway, the tuxedo, must have picked it up from either a stray that wandered in the yard or perhaps a neighborhood cat that passed through - although I've rarely witnessed either and I work out of my home.
For me it was peace of mind to have Carmen and Voodoo vaccinated - the potential benefits outweighed the potential risks. Additionally, Gateway's illness came on suddenly and was fast and furious. He was a 13 lb. muscular cat and was gone within a week. I wanted to avoid repeating that scenario as much as possible - it took its' toll on all of us here - Carmen and Voodoo, included.