Smiffy,
what seems apparent to me is that you are looking at it through the eyes of a general coarse angler. In that respect, I wouldn't necessarily disagree with you. However, my dim and distant days as a full on carper give me a different perspective. A "runs water" can prove that rigs work in a few short hours in a way that weeks, or months may not on a hard water. There are people out there that spend months, even years, on rock hard waters without a touch. It's not my idea of fun, but it happens. I don't blame them in the least for having the occasional trip to a "runs water" just to prove that their rigs are indeed capable of converting pick ups into fish on the bank. It can show you that rig mechanics are working as intended in the way that fish are hooked (not something I've ever known a general coarse angler to be concerned with). If nothing else, it gives them the confidence to keep plugging away on the tough waters in the hope of something special.
As far as taking things from general coarse fishing into (proper) carping on rock hard waters, yes, you can. I rather enjoy doing just that. There's nothing better than taking beefed up "noddy" methods to a specimen water and leaving the biteless bait and waiters frustrated after a few short hours. You may be surprised just how well you can do on rarely seen methods and baits, on waters deemed to be very hard by the full on carpers. The biggest issue is finding such a venue that actually allows lighter tackle and methods to be used.