Tillandsia's grow and flower just fine without any added fertilizer. I grow them with and without fert's. the only difference I notice is a slower growth rate. I have also found that in most cases spraying them even daily isn't enough for them. They usually require a nice soak for a couple hours a week. All in all they are a fun and easy plant to grow. Hope this helps a little.
Yea, fertilizing is not super necessary. Depends on the mineral content of the water you wet them with. I'm just passing on the recommendation of the nursery.
As for watering them, it really depends on your climate. I'm in central FL where it is very humid, and we water ours once or twice per week for just a few minutes and they do great. The indoor ones we just run under the sink a few times per week.