It's almost impossible to keep blight from showing up on the lower leaves by this time of the year, so it does make sense for folks with more serious blight issues to take steps like sprays to keep it from progressing.
Healthier plants absolutely will remain productive despite some blight. Warm, muggy conditions will always have a negative effect if they last for too long, but keeping the plants pruned and allowing air to flow throughout the plants is a massive help. I mentioned earlier that I prune all suckers until the plants are 7-8' high (mid-summer or so) and I also get rid of lower leaves is and when they develop blight - this keeps the air flowing nicely (and I find it also helps with production in general).