you may already have the information you want. but I thought I would add my comment.
I went to a concert there last year...we drove and parked there easily. We went in one of the side roads just before you come into Twickenham town centre, it had parking restrictions, had to buy a ticket but wasn't expensive. Was about 10-15 minute walk to stadium through the town, but well signposted (just follow the crowds).
Hope that helps a bit.