I don't really care about Toy Story, but I do think about milking series.
It appears as ideal to stop at the highest point of a succesful series-be it games, films, books or music albums.
If the series is continues after that point, it quickly comes across as 'milking the product' for money.
However, I think you should first look at why the series was started. Was it for money? Then there is a chance they're milking the product for more money. But in the case of music, bands often just make music because they like making music. They will of course release an album with their creations, because some money is always nice. And maybe they actually do it for the money then, but that''s simply because you need to earn it someway, and you may not have time to make a lot of music and have another job for the money. Then they will keep making music and releasing albums until people get tired of them. Now a band is at its highest point. Is it still milking for money if they keep going? I don't think so. I think you should keep making music as long as you like to, and just not give a rats ass about your legacy. Who cares what people think of you? As long as you have fun making music. The money and the fame just comes with it. And then only sometimes...
Just thought I'd share that. But I don't know about Toy Story. =|