Not a Parish councillor, but I've been involved with our Communuty Council (the Scots version of a Parish council, I think) over proposed school closures. I've enjoyed the meetings I've been to especially the local politics and who bears a grudge against whom, tee hee!
The CC are lending support to our campaign to keep our local school. They do indeed consider and comment on planning applications, if they will affect the area in some way. They have at last got a speed restricion in our village, hurrah. They make major contributions to the council 5 year Area Plan, are working to draw up a footpath network in the area and support community activities in various ways. Nothing is mind-blowing stuff but they are things that help make day-to-day life better. I'd consider being one myself if we weren't moving. HTH