>Running 101>Struggling at the Moment
Speed workouts and tempos are for pushing yourself. Per Daniels, they should comprise (max) 8% and 10% of your total weekly mileage, respectively. I wouldn't say he's the final authority or anything, but it gives you some place to start. Me personally, I get equally good results with just 5% at 5K pace or faster, if I'm racing 10K or farther. I enjoy tempo stuff and my body puts up with it well, so I push it to 12-15% some weeks, but not every week.
It's unclear whether you would've become faster by running more miles total at an easy pace or doing what you did. Running lots of faster-paced workouts is satisfying because your progress is more evident. Maybe you would've seen equal or greater progress by running easy every day, and testing yourself at a 10K race once a month. One problem with the latter is you might not have stayed motivated if you saw progress less frequently. You have to balance your body's need for time and recovery with your brain's need for reward.
Gang Name "Pound Cake"
My understanding (limited I'm sure) is that stress provides the stimulus for the body to build a faster more powerful engine. But... its really hard for the body to build when it is constantly being torn down by the stress of training. The body mends while sleeping and resting. It also can mend on recovery and easy running days with the increased blood flow can help remove junk from the body following rebuilding.
To little stress and you don't get better. To little rest and you also may not get better, in fact, you may break down. That's why most training programs for us non-elites, alternate "workouts" or "sessions" as the brits call it, with easier running days or rest or cross training.
While Ryan Hall might be able to hammer it 5 or 6 or 7 days a week, us less gifted should likely keep the faster and/or longer stuff to 2-3 a week. Three workouts: one tempo, one interval or hills, and one long is PLENTY of quality for the 99% of us. For newer runners, one long and one faster workout is plenty as well. When starting out or during off racing season, you can get fitter and faster without much fast running at all - just easy running with some ending striders, and with one weekly long run.
Some world class runners can run 200 miles+ per week including speed sessions. I've heard of one guy who did more than 300 miles a week for about a year before dropping down to his regular 180 to 240 miles per week. That's a guaranteed injury for 9,999 out of a 10,000 runners. While it is interesting to read what some people can do, most of us don't have the genetics to follow their training to closely. I wish I could do workouts like those top athletes. It's really hard to be patient. But when I start to feel run down or that I'm carrying over too much pain from workouts earlier in the week, I start thinking I need a few more easy days or a couple or three of off days. Get injured and it might be 6 months of forced off-time. Got to avoid that.
2014 Goals: First Marathon - BQ2016 <3:40 - 1/2M <1:45 - 5K <22:00
2014 Marathons: 05/04 Flying Pig (3:49:02) - 09/20 Air Force - 11/01 Indianapolis Monumental