Will these seeds be useful for birds?

If you leave the plants standing, I'd expect to see winter songbirds.
If you are planning to collect the seeds..... I wouldn't know.
At my house, I commonly see songbirds going to town on the natural wildflowers....

I don't think I've ever noted either visited by birds; however, New Eng Asters are one of, if not, very best of wildflowers to attract multitudes of pollinators...butterflies and bees overwhelm them in September.
Goldenrods are keen at attracting wasps in particular.
In my experience wild seed attractants for birds would be Purple Cone Flower and Maximilian Sunflower.

Funny.. I thought I had replied here with some links. I must have replied on another thread.
Illinois Wildflowers does a god job listing faunal associations. Relatives in these genera seem more important for the insects they support,and THUS birds eting the insects, than they think as seed for birds.
I agree, jmorth, the variety and number of wasp things etc, on goldenrod, is incredible.

I have a patch of giant Rudbeckia I am sure hoping birds eat all those seeds. They spread like mad just by root alone.