When you mentioned how they produce a lot of thin, new growth without flowers, my fertilizer antennae went up. My guess is that you are feeding your lawn, and the lawn fertilizer (which is formulated to produce leafy growth in grasses) is encouraging your wisteria to perform the same way. Do not apply lawn fertilizer within 10 feet of the base of the wisteria. It may take a couple more years for the vine to change its habit if youve been fertilizing for a few years.
If that is not the case, then look overheadis the wisteria growing in full sun? Nearby trees that were small when the vine was planted may now be shading it.
If it were mine, I would also undertake a rigorous pruning program. Keep cutting back all new shoots this spring and summer, not allowing them to get more than a foot long. Then, cut them back again this winter limiting each young shoot to about 4 buds. I would also use a sharp spade to cut into the soil about one foot down around the plant, 2 feet away from the trunk, severing all the roots. That may shock the plantwithout hurting itand encourage it to bloom.
Complaints about non-blooming wisteria are common, so youre certainly not alone. You may need to do all these things to get the plant to bloom again.