Lucy excitedly braying "It's Ruta Lee, the movie star!!!" is as good a marker as any for the end of Lucille Ball's reign as TV's funniest and most valuable star, and the the start of that tired recycling of threadbare, out of date shtick and punch lines that comprised the latter part of her career.
I "love Lucy", and I'm not trying to be a jerk, but using the same writers, the same themes, forcing the same old slapstick, only slightly reworded gags, madcap schemes and antics, etc, from the past onto a new decade and a leading lady now aged past the point of being crazy-funny in such situations and began to look crazy-pathetic-sad, had to yield, to put it mildly, diminishing returns.
I guess that with "The Lucy Show" it's a little understandable (if hardly admirable) that Ball would feel safest sticking with what had worked before. By the time of her last, dismal effort "Life With Lucy", with it's corny lines and creaky (literally) physical "comedy", there was no excuse--neither for her not seeing that transplanting the old onto a new era couldn't work, and for no one around her telling her so. Compare her set, stubborn clinging to the past with the aged stars of "The Golden Girls", adjusting and changing and moving to new forms and structures of humor, using their gifts honed over many years, and applying them to the present.