I agree popsider that some 'plodders' and other runners too, are limiting their own achievements. It's important not to compare your own running to others when measuring progress (although hard not to do)..
I am a slow runner and although I had read various articles on visualisation etc, just thought it was for hard/fast/very competitive runners. However an experience a couple of years ago changed my mind.
I was running the Robin Hood Marathon, at my usual 5 hour + pace, when at mile 22ish a police motorcyclist offered to lead me for the next mile or so along the coned section of road, where we turned through Notts Forest ground. So there we were, the police bike with blue flashing lights, the traffic at a standstill on the otherside of the road - and suddenly I felt really proud and important, my head automatically went up, the pain in my legs was forgotten and I started to stride out down that road, I ran my fastest mile of the race. I thanked the MPC, and finished the rest of the race in my best marathon time that year, and from that point on I have continued to set PB's every year in various distances, mainly because I believe I can do it and visualise myself striding along. Before I just told myself that I was doing too many distance events to improve on time and this was affecting my shorter race times - rubbish. I just never thought I could do it.