In a word, no. Some "refurbished" aircraft only touch certain parts of the cabin experience, but Delta's refurbishment of these particular aircraft was nose to tail - there's essentially no legacy cabin fitting visible anywhere at this point, even in the lavatories or overhead bins.

I suspect they invested heavily in them because a true replacement is in the far horizon: Boeing is working on a new "middle of market" aircraft to target the 757 replacement market, but it's still at least 5-10 years from being ready. Delta has dabbled in purchasing some A321s, which can be a partial replacement, but they haven't shown signs of betting the entire fleet renewal on the type. The 757s will be around for years to come.

I also haven't seen any instances of the 757's dispatch reliability starting to suffer; Delta deeply understands how to maintain these aircraft and parts supplies are plentiful across the system. So no extra chance of a flight delay over flights operated by other narrowbody aircraft.