For Blissey to be most effective, she should sit somewhere in the middle of the gym. In my area, that in itself requires a lot of candy, but I want to have a Blissey to put in gyms, now. In my situation, I would focus on maxing out the one you have.
Conversely, Blisseys are big investments. If you don't want to use one, now, you could work getting a perfect one to invest in once you have it. That might turn into a long term project, and things may change in the meantime, or you might be happy with the result in the long term.