I agree that kids just basically want to be where the action is. The only time kids (from the various families I visit) use their play areas/rooms is when other kids are over, and they want to show them all their toys. Other than that, they want someone to be near them, to watch them play, to interact with them etc. I plan to have a play area in my living room (we are blessed with enough room to do so...) and not try at all to keep the toys in a room where I am not. I want to see how they are using the toys, and also how much of a mess they are making before cleaning up the last mess they made!
Ideas I want to use:
Keep sets of toys in boxes with lids- this is something I totally will use clear plastic boxes for. I want to keep sets of toys in boxes on a shelf, and a few boxes can be down at a time.
Keep only the toys that the kids play with- some kids ignore stuffed animals, some kids play with them constantly. The kids I babysit here at my house, grab all the stuffed animals they can find and they set them all up on different books, as a Zoo. BUT- if the stuffed animals or other toys were not being used, I would sell them or donate them.
Keep age appropriate toys together, and put them away after that age has passed.
Teach kids to pick up their own toys. My friend has the same problem as you (Cathi/OP) but her kid's play room is upstairs, and they are constantly bringing the toys down to the main level of the house. She says that is fine, as long as they take them back up with them when they go. Well, she has it almost down pat, and rarely carries toys back up those stairs herself. The kids know that they need to do the job themselves.