G'day Steve,
Maybe others see things differently, but I do not feel a massive influx in people contributing raw, valuable text to our encyclopaedia, which is something we're quite short of. We have lots of people joining us to help delete, categorise, clean, or write about their own pet topic - but do we really have so many helping to expand on our existing topics?
I agree. Heck, in some cases I see the same *name* (singular) editing an area of the encyclopaedia with me.
There's also the issue that an editor's "own pet topic" tends also to be the "own pet topic" of thousands of other people. There's very few people who are fascinated by the mating habits of gibbons and *also* want to spend hours working on Wikipedia, but there's an imperial truckload (that's more than a metric truckload, for those wondering) of people who want to talk about trains. Not all pet topics are equal.
Cheers,