Although I don't personally experience a decrease in tastefulness, I do experience a change. The first cup in the morning, when I'm breaking my fast, encounters hungrier taste buds.
With the current heat wave, hot coffee in the afternoon is on its face not a necessarily appealing proposition even if one is in an air-conditioned environment because the human body has warmed up as the day has progressed. Even when I'm cold, coffee so hot that it must be carefully sipped is too hot for me. This morning's pot was poured back and forth repeatedly between the carafe and my mug until it had cooled enough that I could take big sips. By the time the sun is high today, I won't want coffee that's too warm to gulp.
Roast: Behmor; Grind: Baratza Encore; Brew: Sunbeam C30C vacpot