A couple of things to keep in mind before considering the issue and process of overseeding:
1. NTEP ratings are, for the most part, subjective comparisons of cultivars of the same type of grass at a given test site and a particular cultivation method. (water, fertilizer and mowing height). The ratings are usefull for comparing cultivars of a particular type/family (e.g. TTTF, or rye, or KBG) at that test site. The ratings are not particularly useful for comarisons between test sites (other than comparing how cultivars do in the conditions between the test sites) Most importantly the ratings are not useful/valid for comparing different types of grasses (fescue vs KBG) even at the same test site.
2. KGB is more susceptable to drought than fescue. KBG generally goes dormant quicker than fescue. (although it is capable of recovery after a long period of dormancy). If you are not irrigating enough to keep TTTF out of dormancy, KBG is going to do no better at avoiding Summer dormancy.
3.. Unlike KBG, fescues have very little, if any, ability to spread. Once it dies (from disease, estended dormancy, whatever) it is dead. So it is unlikely that it is recovering from thinning out in summer and filling in come Fall. What you are observing is either TTTF recovering from a short dormancy, or you may already have some KBG in your lawn.

This post was edited by grass1950 on Sat, Jul 27, 13 at 10:32

Thanks grass1950.

I don't believe the TTTF is going dormant, I believe it's just weakening and thinning over the course of the season. I am irrigating. I've been trying to balance my cultural practices for years and can never seem to get it just right. This year nature has been working against me - wettest June on record in NJ I believe - which has resulted in a lot of fungus and die-back;

It sure does seem to perk back up in the fall, for whatever reason. You're right - I probably do have some KBG (most of the lawn is original to the house), but it's clearly not an optimum variety because it doesn't maintain its color and vigor as some of the nicer lawns I've seen. It's not bad, but for the effort and irrigation I put in to it, I would expect better.

Is it a waste of seed to try to infuse some better varieties of KBG in to the lawn with a fall scalp and spread?

As to your original question: Many have had satisfying results from overseeding in the Fall. Success primarily depends on sunlight reaching the seed and proper irrigation for the 3-4 weeks that it takes for KBG to germinate. As would be expected, seed will take best in bare and thinner areas of the lawn. (keep in mind the need to match growth rates, color, and blade width between the new seed and the existing turf). I, personally have had very good results from overseeding. So, in my opinion overseeding works and is worth it, but results will vary.

What puzzles me about your sittuation is what condition your condition is? It sounds like your major issue is loss due to disease. People particularly in the East are reporting increased brown patch issues this year with their TTTF lawns. To avoid brown patch damage you need to be proactive with preventative fungacides and reactive with curative fungacides. Brown patch usually (but not always) does permanent damage to the turf and as I said, TF doesn't possess the ability to spread and fill in in the Fall. So I'm a bit puzzled by what you are reporting.
Anyway, the best thing to do about reoccuring disease problems is a preventative and currative fungicide regiment. Weak grass is more susceptable to disease, so you should see if there are any weak links. Get a soil test and see if you are low on any nutrients.
The greatest improvement in turf will come from proper mowing, irrigation and fertilization.Make sure your turf is getting proper irrigation. Too much irrigation can be worse than too little, Do a screw-driver test to see if moisture is penetrating (poor water penetration (hydrophobia) can often be repaired by shampooing) If your soil is not holding moisture--add organic matter.
What types of fertilizer are you using and what schedule?
How often are you mowing and what height?

mooch91,
I did a little research and pulled up some university turf fact sheets on brown patch. Although some report that brown patch "sometimes" results in turf kill (Penn State-and this was my experience with my TF lawn in the 70s), the majority report that it most often results in severe thinning that will recover in the Fall. This does sound like what you are reporting. As the pathogen remains in the soil and thatch layer from season to season, this would explain your continued problem. Applications of phosphites (Heritage or Insignia) can prevent reoccurance. Per my inquiries above, proper mowing and fertilization can help prevent outbreaks or at least limit severety.