I haven't had my Scalpel for very long, but in response to your concern about the chainstay delaminating from chain slap, I solved that problem by putting on a Bushwood chainstay protector (basically 3mm neoprene closed up with velcro). The Scalpel comes with a fairly thick plastic transparent chainstay protector that can be replaced when it wears out, but like you I don't like the idea of the chain slapping on the chainstay, plus I hate noisy bikes.
Cannondale also asks you not to use poor gear ratios (ie small chainring & smallest cog) as the chain will drag across the chainstay, or to fit different sized large chainrings as the tolerances for front derailleur setup are so fine. Having said that, it sounds more trouble than it actually is, but as you rightly asked, take the advice of long term owners.
In terms of durability, I wonder how heavy you are? I'm only 68kg (150 lbs) and pick my way through obstacles rather than blasting through them, so I can make a light bike last a long time.
Cannondale also asks you not to use poor gear ratios (ie small chainring & smallest cog) as the chain will drag across the chainstay, or to fit different sized large chainrings as the tolerances for front derailleur setup are so fine. Having said that, it sounds more trouble than it actually is, but as you rightly asked, take the advice of long term owners.
In terms of durability, I wonder how heavy you are? I'm only 68kg (150 lbs) and pick my way through obstacles rather than blasting through them, so I can make a light bike last a long time.