Any trash picked up is a good thing. But I'm afraid big cleanup days just don't work as a whole solution. I've participated in them. The local riff-raff will throw beer cans out the day after you leave, and keep doing it w very day until the next clean up. I think for things to change we'd need a large body of people committed to picking up a little every time they see it, combined with big clean-up efforts and maybe some education.
The idea I have kinda started while fiahing with a buddy. We were trolling around fishing, and he casually ran by a Gatorade bottle and threw it in a bucket in his boat. He never stopped talking or set his rod down. I mentioned I usually ended up walking out of the squirrel woods with trash on my vest, and we got to talking about how if everyone with a sportsman's license did that every time they went out, there wouldn't be a beer can left in a few years.
Small acts have a cumulative effect. Nobody is dumping huge loads of trash once a year. Why clean it that way?