Hichy:
Yes, I think you can hit your goal of improving you 5k time by a minute by next year, perhaps more. I know you are trying to be realistic about your talent, and, therefore, have made a strong commitment to doing what it takes to reach your goals, but running a ton of miles before it is time is a mistake; in my opinion. The key is to arrange the miles in such a way as to maximize development. Additionally, as "quality" poster pointed out, running some faster training is key to progress. I do not advocate, however, hammering all your current miles. That would be counter-productive.
I will give you an example of a runner that I coached. He was a sophomore at a small college. He had run for 6 years at a competitive level. He was proud of his high school 2-mile p.r. of 9:52,done on 50-60 miles per week consistently for the second half of his junior year and all of his senior year in high school. He was a mild-mannered fella externally, but internally he had a strong desire for success. After one year of collegiate running, Ted had modest progress despite his hard workouts and mental toughness. He trained all year, except for an annual week off at the end of the fall and and at the end of track during finals week. He was coached by well-intended fellas who in retrospect did not understand how crucial it is to do three things: 1) vary the training paces, 2) do long intervals, 3) and do tempo runs. I volunteered to coach the track runners and jumpers in the winter of his junior year of college and found both Ted and a few others, far less talented than most high schoolers, eager to improve, but frustrated with the amount of progress they had experienced.
I won't go into the progress and workouts of the others, though at some other point if you want to I can, but for Ted, I changed his montonous training to one of varied pace and varied distances. He had been running mostly 8-10 mile runs at moderate to hard paces during the off-seasons and doing a lot of 400s on the track during the season. I did not alter (the first season that I coached him) his 60 miles per week but I did vary the distance more and the paces too. Instead of running a steady 6:30-6:00 pace for his typical 9 mile route, I had him run 7-7:30 on his everyday, maintenance mileage runs (based on his recent 5k road race at Thanksgiving of 16:17). I calculated his training pace for those everyday miles at 5:15 pace (approx. pace for 16:17 5k) divided by .75 to .70 (5:15 = 315 seconds / .75 to .70 = 420 - 450 seconds which is 7:00 to 7:30 pace).
For his tempo runs, as a 5000m man, I had Ted run medium length tempo runs on every Monday during a 10 miler. So, he ran about 5:50 to 6:00 pace for 40 minutes...or basically on a 6 mile loop that we normally ran, plus a bit extra around the warmup loop. On Tuesday, he ran at his easy pace 7:00 to 7:30 for 7 miles, as he did on Thursday and Saturday. On Wednesday's 10 miler, he ran a short tempo run of 4 miles at 5k pace divided by .93 which for him was 5:39 per mile. On Friday's 10 miler, he ran a long tempo run of 8 miles plus a warm-up and cooldown mile each. His 8 mile long tempo run was 6:02 pace. On Sunday, he ran anywhere from 4 to 10 miles on his own at his normal, easy DP of 7:00 to 7:30. Ted did the above plan during December and January, no variation. In early February, he ran in an indoor track meet 3000m run recording a best of 8:48 which is equal to 9:27 for 3200m. He had a p.r. by 25 seconds. Cool, right? The next week, he ran 15:22 for an indoor 5000m on the very same track and beat several good runners.
The rest of the outdoor season, Ted ran in seven 5000m races, most of them in challenging cold and windy conditions. His slowest time was 15:32 and his fastest 15:18. We realized that weather was a big hindrance when Ted had beaten two guys who had run under 15 minutes for the 5000m the week before in the South in 65 degree and calm weather. Incidentally, Ted only changed his Wednesday workout during the outdoor season to that of 4 x 800m at 5k pace with 800m runs at his steady 7:00 to 7:30 pace. That was it. The next year, we varied the training he did even more, upped his mileage to 65 to 70 per week, and he ran at Nationals for XC in 25:13. Not bad for a guy who looked a bit overweight and more like a stocky wrestler than distance runner. By the way, Ted's p.r. for the mile was 4:38, so he had very little talent compared to most runners he competed against. He did not, however, crank out the big miles, although over the years it would have been a natural progression for him to do so. I like to add about 10 miles per year to a runners training scheme after their initial three years of running in which mileage can jump fairly quickly from zero to 50 or so without any problems.