It sounds like I'm similar to the previous poster. I've run at least 20 road races in from 1641-1730 and one 5k indoors at 1639 (my old PR).
This weekend I ran just under 16 (1555). Here's how I did it:
First, I broke my foot 2.5 years ago and had to give up running. In my quest to not get fat, I actually lost about 10 lbs. Some of this was from the large volume of cross training and cycling, but it was mainly from a better diet. I cut out most soda/beer, and really try to eat fruit and/or veggies with every meal.
When I started running, it was a SLOW build up. It took me 3 months to get to 35 miles/week. At this point I started training again, and worked miles up the the 40s with quality.
I wantede to run sub 16, so I ran two TTs on the track to see where I was at. 1654 the first time, 1635 two weeks later. The second included perfect conditions on a nice outdoor track with my uber-cool wife yelling out splits.
Honestly this was a little frustrating. The 1635 was on the heals of 2 months of really quality training (in my mind). I had resigned myself to running high 16 road races forever.
Then the next week a casual acquaintance offered to coach me. I thought why not.
He did a few things very specific for me.
1. Very few long runs. I think I ran over 10 miles only twice during the 16 weeks I followed his plan.
2. We worked on my weaknesses. For me this meant I would train like a miler. Doing speed sessions with walking instead of jogging rest at speeds much faster than normal.
3. Challenging me to run times in workouts I didn't think I could do. An example would be repeat 800s under 225 or a workout starting with a 452 mile followed by 1000s under race pace.
4. Keeping it simple otherwise. 4-5x times a week I ran 6-7 miles at 630-700 pace.
5. Change when necessary. When the weather was bad, we moved workouts. when I got sick, we made things easier.
6. Get in a good race. I couldn't have run under 16 alone. At the same time, know youl will have to run even. 309 was my fastest K, 312 my slowest.
My final take away is that I didn't needmore mileage. I needed a healthier lifestyle and focus. 50 miles/week was enough for me. From this thread the idea that everyone is different is certainly supported.
GOod luck!