The main concern with cables touching chain stays is cosmetic damage to the paint over time and maybe cable rattle. On some old bikes, they actually routed the cables directly against the bottom bracket and had welded guides to keep the cables from drifting around under shifting stress.
On the bikes I build for the non-profit shop I work at where we refurbish pre-loved bikes, adding "donuts" takes care of both issues.
Another solution is to add a plastic sleeve to the exposed cables. You can also

buy cable/housing sets that include the sleeves that have integrated housing stops and these systems are great for keeping the crud out of the housing, thereby keeping shifting performance at its best no matter what the road or trail conditions and the cable and housings will last longer as well (so the extra cost of these systems is paid back in longevity. The system I have on my Hillborne is the GORE RIDE ON CABLE SYSTEM but other systems are available.
I just built my 55/700 Sergio Green Atlantis and I'm trying out different derailleurs on it. For now, I'm just using donuts for the rear derailleur cable at the seat stays (and the rear brake cable that runs along the top tube). Once I've finalized the derailleur set up, I'll likely use the Gore system since I have a set already.
Peace and enjoy your new Clem!
Thomas