Digesting Dan Bricklin's "When The Long Tail Wags The Dog" takes a long time, but is well worth it. Bricklin makes an argument for generalized tools being the big winners in hyperabundant, hyperdifferntiated economies, commonly referred to as Long Tail markets. If you don't track this stuff, read as "market with a ton of niche product of high value only to a small audience." The club DJ 12" vinyl dance record market might be an example. In any event, Bricklin's argument rest on general tools providing a wider array of options, including any unanticipated capabilities that you might want.
Extrapolating Bricklin's argument to webfeed aggregators, an extremely flexible aggregator that exhibited one or two compelling uses out of the box could be a big winner. So all the meme-tracking tools might be barking up the wrong tree in the long run. Then again, designing for extensiblity in an aggregator is still in its infancy, and designing for extensibility in general is hard.