Hey mate, I love the challenges that your articles lay down, and in this case controversy.
I agree with your sentiments, and with Hans, in that reputation required can be so context dependent that on occasion it can make even aggregation not useful if its not broad enough.
e.g. if you are deciding to lend to some thing to some one for free on a gift culture website, the question isn't just will the item be returned in good condition, but it may also be how has the requestor contributed to the community? An Ebay rating isn't useful for that.
Guess that's why aggregating across a range of different services is ideal, as you suggest :)
Sent from a mobile device.