PB - I guess whether it's good or not depends on whether you feel good and whether you're happy with your running! If so I'd say don't change it :-) You can't be doing that bad if you've kept it up for 10 years.....
Me, I only started running at different paces when I started the RW training schedule for the autumn HMs - I did Windsor on 29 Sep, and as it was my first HM I wanted to make sure I got round OK. Before that I used to run for 40-45 minutes, at whatever pace felt comfortable depending on weather, mood and tiredness....but I found that following the training schedule really helped my running, so I'm going to keep trying to include a speedwork session every week at least.