I, too, have only seen one honey bee foraging on a single dandelion flower. Maybe they like to save the nectar sources closer to home for bad weather or nectar dearths? It's annoying though, because if they don't take it, some other bee will!
Haha, nice! We let the dandelions bloom, too. I've only seen one honey bee on a flower, though... I have no idea where they are foraging, maple tree sap, probably, but they are coming home laden with pollen and their honey stomachs are full, too, I can expect.
Yes, the other bugs will love it... Not always a good thing. Make sure that you keep the weeds trimmed down at least foot around the sides and back of the hive, and maybe three feet in front. They'll need their flying room to gain altitude, and it's much easier to work bees in a trimmed area.
Watch out for ants, too! Ants found my nuc in only 12 hours. I read that normally bees can keep down an ant population, but if they get overrun they will abscond. We treated them by thoroughly shaking cinnamon over the ground, hive cover, and entrance platform. The ants don't like it, but the bees don't seem to mind. Now that the bees are in a Langstroth hive on a high hive stand with four legs, we can make an oil "moat" by putting each leg in a can of motor oil.