He probably got worse in the conventional sense, that call preserved above of Maris' 61st HR seems really good. He was endlessly entertaining, though, and I can't imagine these guys went through more than a fraction of his 40 years of broadcasts.
I've got a Red Sox-Yanks game from 1961 where he's trying to play it straight, and he's pretty good except for the occasional Holy Cow!
They probably don't have many games from the 1970s. I suspect that might have been the zenith where he was still a competent announcer on the fundamentals (and just a younger, more energetic man in general - he was 75 in 1992, and he didn't seem that spry for 75) but with the Scooter charm and humor. I think as he got older the Scooter took over full-time. Not that I would have complained, he was hysterically funny. I have a piece of a game where there's thunder storms and Scooter's all but running out of the booth with fear while Bill White's trying not to die of laughter.