I think there is definitely a point of diminishing returns, especially for touring where durability matters more than lightness...

My ideal build is Chorus11 shifter driving a Shimano XT 9speed RD on DT Swiss 350 hubs laced to TK540 rims. Crank would be a 42t-26t Sugino OX801D with a Shimano CX FD or maybe an IRD Alpina FD. Handlebars would be Salsa Cowbells. Tires would be Schwalbe Marathon something or anothers, probably 35mm or so. Disc brakes, probably TRP Spyres. Saddle is Terry Liberator. Seat post is Thomson. Pedals are Shimano a530. Tubus racks, SKF fenders... hmmm take the hub choice back, I'm going to lace a SON dynamo on the front and a White CX hub on the back for the sake of matching.