Pollinators don't just go willy-nilly from flower to flower. In fact the smell, color, and location determine what the pollinators will forage. Some pollinators are exclusive to a single species, others are gathering scent. Pollinators aren't exclusive to Hymenoptera, beetles, flies, bats, and birds are also involved in the act. Flowers having color, scent, and nectar are useless to reproduction, unless there is an ulterior motive, in this case attracting a biological mechanism.
No nectar, the flower will have to have a pollinator that expressly seeks the other factors to make the expense in flowering economic. I found the numbers once, but am too lazy right now. About 17% of Apis Mellifera gather both pollen and nectar at the same time.