I vote for powering up what you have. Even a suboptimal moveset Blissey is still a better defender than anything else, and will strengthen any gym she goes in.
You could use all you candy on evolves, and still not get the moveset that you want.
At some point if you wish to maintain more than 1, then you are already going to need to buddy up to get more candy...so keep what you have for maintaining what you have.