Realize I can't see the yard, but here's my 2 cents. If the lawn isn't uneven, why go to the expense of topdressing. You said there was patches of good grass so why not heavily aerate/scarify the bad areas. Also, what type of problem caused the bare areas; weed infestation, disease, pest's etc.. . I don't think you're too late unless the soil temp is 60>. If this is a regular acct., long term you should do a soil test. This will tell you what is going on in the soil and reveal, if any, problems with pH and nutrient deficits. I use A&L. They're local here. Test with reccs is only 9.95 (here). Basketball sized patches sound like a disease since you haven't had a hard freeze yet to kill off summer weeds.