I'm going to try to take a different tact then Zeke and Ryan despite the fact that I agree with what they're saying.
Randy, You may indeed be, as you say, “built more for endurance and less for speed”, but it seems to me that you've never bothered to commit to making yourself faster. You have an amazing consistency and ability to commit to the marathon distance, but you refuse to make that same commitment to shorter races. This is fine, for the most part, because you seem to only care about the marathon, but you are limiting your possible improvement even at this distance. If you cannot run more then 4 miles at 7:04 pace (and I realize you probably could if you tapered and prepared the same way as you do for a marathon) you will never be able to run 7:15 pace for 26.2. It will not happen. Now, you can continue to do your consistent, proven training and likely drop another 4-5 minutes off your marathon time next year, or you can try something else. It depends what you want for yourself. If you want to continue to consistently approve with little risk…keep doing what you're doing. If you want to see if there is a better way and, possibly, find that you have much more potential then you previously thought, then its time to shake things up. Heres what I propose.
Build your mileage back up over the summer to as high as you feel like going. Then, instead of keeping it in the 90's through December and Philly, knock it down to 60-70 and run those tortuos intervals and other such hard workouts in a serious attempt to peak for a 10K race. Forget Philly, you dont need to do another marathon at this point. Forget about the mileage during this time as you have a 4 YEAR base. Its time to run FAST and learn how to embrace the burning lungs, I feel like I'm going to puke type of workouts. After you bury your 10K PR, you can build the mileage back up and do your normal marathon push. You'll be more efficient, feel more comfortable at faster paces and likely be glad to drop the intensity (though you might find you keep more then you would think).
Doing this, maybe you set a HUGE PR, maybe not, but I think you owe it to yourself to give it a go. I'd be shocked if it didn't end well.