Pleasure bay isn't under underutilized. The whole area from Castle Island to Carson Beach is well utilized.
I would add a concession stand where the ice rink is since Sullivan's has lines out the door. Although, I remember reading a while ago about someone trying to open a restaurant along the waterfront near there and the NIMBY's crushed it. Maybe you could get away with a concession stand open Friday through Sunday during the summer.
There are a few areas around Castle Island that could sue some sprucing up.