If you're in a high-risk area it might be worth doing...however, the lepto vaccine is not always effective because there are many strains of leptospira bacteria that can cause disease and the various lepto vaccines protect against between one and four strains. It does prevent those strains from affecting the vaccinated dog very effectively, if those are the strains the dog comes in contact with.

The lepto vaccine has a reputation for causing a lot of adverse reactions, but newer versions of the vaccine don't show a high incidence of reaction. I believe it was the way the earlier vaccines were made which caused the problems, and the newer versions are more refined. Here's an article with more info:

http://www.cpvh.com/Articles/88.html