Personally, if your old life "died" and you received baptism as an outward expression of that, I would think it's enough, but if you wanna get dunked again, I'd say go for it, it can't hurt! :)
I was baptized a Catholic as a baby (unwillingly) and baptized in a Baptist church willingly at the age of 12. My baptism in the Baptist church was enough for me. I knew I was getting baptized as a symbol of my old life dying and a new one beginning with a relationship with God. I'm not interested in getting baptized with the JW's because I think there's too many rules and provisos that frankly aren't biblically sound. Besides, I'm turning 40 this year and I'm waaaay past jumping through hoops for man's rules.
If you do it, make sure to take pictures! I regret that pictures weren't taken when I was baptized, as it was a very special time in my life and my relationship with God.