Thanks for your responses, DivineR & TeeHee. I'm always interested to hear the experiences of others.
Up to this point I've seen three neurologists. Two didn't really mention diet and exercise at all, but the other gave me some useful unofficial tips, which have had a positive impact on me:
1. Eat more anti-inflammatory foods.
2. Cut out dairy.
3. Drink coffee.
4. Add turmeric / cumin to meals where possible.
5. Exercise daily (where possible).
I think there is a stigma attached to talking about the benefits of diet & exercise for those with PD. I'm not suggesting that lifestyle factors can cure PD by any means, but what one eats and how active one is certainly affects levels of dopamine in the brain (among other positive impacts). Of course, everybody's situation is different, but for now a plant based diet and daily exercise significantly improve my rigidity/stiffness, sleep patterns, slowness, back pain and energy levels throughout the day.
Based solely on my own experience thus far, I'd advocate considering lifestyle changes as a significant factor in helping reduce PD symptoms. My hope is similar to TeeHee, in that I'd like to keep medications to a minimum. It's a no lose situation as far as I can see, because even if a healthy diet and exercise have zero impact on one's PD symptoms, I doubt you'd find a Doctor who would discourage such positive lifestyle changes for overall health.