I would also be very surprised if it turns out that there are a whole lot of bloggers who constantly need ideas from others to write about.

Most bloggers i know, write because they are genuinely interested in an activity/thought/event. If someone writes about something they are not really interested in (or knowledgeable about), it would be plainly visible. (One of the exceptions i can think of are people who write pure fiction like short stories on their blog ala writers.)