Over time, as a bottle is consumed the wine is exposed to air and my brain is exposed to alcohol. I’m convinced that both have effects independent of each other. Usually positive in moderation and negative in excess. The trick is in knowing where the line between moderation and excess lies. It’s different for different wines. Experience helps.
In my limited experience, decanting Champagne doesn’t help. These were old-ish bottles (20-30 years). I’m willing to give it another try with younger ones.