I do let my basil flower in the fall because I save the seeds and start them next year. Actually, I don't really need to save seeds since it will happily, and prolifically, reseed itself, as will the dill, cilantro, and parsley.
My mint is very prolific and does flower, the flowers aren't anything to write home about. It will cross with oregano (I've yet to see my oregano flower but it produced yucky tasting little minty looking babies last year) so I tend to keep the mint pinched back. Actually, that's not true, I tear them out in great big vicious yanks. Good for stress relief and I think it likes the rough treatment.