Hiya metal!
Have you read the exchanges between Prodromou, and Carter and McCarthy; and then Carter and Cook (all drawn from the ELT Journal, and reprinted in Seidlhofer's
Controversies in Applied Linguistics (OUP))?
Cook makes some good points about cliche vs creativity in response to a rather meandering initial paper by Carter (and Cook's paper in turn elicits a thankfully more concise reply from Carter), namely, what do we expect learners to say and be able to say (he is not in favour of encouraging copying what native speakers say word-for word). Seidlhofer's introductory comments/contextualizations are excellent, by the way.
(There are also quotes re. "Widdowson vs. Sinclair 1991", but only from Widdowson's side, as permission could unfortunately not be obtained to reprint Sinclair's paper. Beaugrande's comments in this regard are therefore well worth reading, at:
www.beaugrande.bizland.com/WiddowSincS.htm, and e.g.
www.beaugrande.bizland.com/henry.htm. You may not be able to find these pages using your current search engine; I found them via MSN Japan searches, using the terms "henry widdowson" and "widdowson vs sinclair" repectively. I could copy and send them onto you or here, possibly

).
These "controversies" in themselves may not help one to decide on which side of the fence one sits, especially if one has not read much (more forceful/polemical, less "negotiated/considered=considerATE stuff) about Corpus Linguistics beforehand (not saying you haven't, metal!

), but they are kind of required reading, and should be able to find a new and wider audience in this new format.
Generally, this whole debate kind of reminds me of Bruce Lee's criticisms of classical martial arts, and more specically, the Japanese concept of Shu, Ha, Ri. I sometimes wonder how far he would've gotten without Wing Chun and the other pre-existing martial arts to help him on his way - perhaps his "genius" simply lay in having the courage to pursue his "own", more "real" path (as Lee himself said, "A punch is just a punch, a kick just a kick")...anyway, with languages, one can't simply appeal to efficiency, and there in fact seems to be a contrary desire to be fancy (trying out your language skills won't get you into as much trouble as literally fighting would, especially if you used the "mess" of classical fighting forms, as Lee saw them, for fighting!), even when there are fancy forms already to use for verbal repartee!
That is, native speakers and sensible students of English don't walk around saying "raining cats and dogs" when there are other more basic - or potentially more colorful/less cliched - ways to say the same thing; we all aspire to be witty rather than wor(l)d-weary, even if we don't always have time to think up something that would kick metaphorical ass better (like I maybe didn't just then when I said "kicks ass"

). That being said, "raining cats and dogs" was doubtless once a hilarious and very individual contribution to some conversation somewhere, that somehow caught on (for some strange reason), especially amoungst foreign learners (good job, whichever idiot taught them this idiom! But then, I guess it will always be hard to know exactly what phrases will show learners the creative meaning potential of the language).
Lee's other philosophical basis - Krishnamurti - kind of irritates me (as does Widdowson, increasingly - does this guy have anything left to say?!

).