[Yip1982]

Some time ago it occurred to me that perhaps there is some kind of symmetry between the two acts of CATS. However, while there may be some kind of similarities, there are also differences. I find this very striking.

-The show begins and ends with full ensemble numbers for the Jellicles.
-Both acts allow the cats with "housekeeping qualities" to let their voices be heard: Jennyanydots in Act One, and Skimbleshanks in Act Two.
-The Jellicle Ball in Act One and the Mistoffelees dance in Act Two seem to provide some kind of climactic apotheosis in their acrobatic feats and exuberance.
-Both acts have set pieces based on narrative poems at symmetrical points. Pekes and Pollicles takes place 15 minutes before Act One is over, and Growltiger is performed and sung 10 minutes into Act Two.

However, there are differences. I think that one key difference is that Act One is more lighthearted than Act Two. It just seems a little more cheerful with the Gumbie Cat, the Tugger and the Mungo-Rumpel antics. Pekes & Pollicles only lends to the merry atmosphere in Act One, and perhaps is much more cheerful than Growltiger in Act Two. Also, Act One showcases the better-off cats - Jennyanydots, the Tugger, Bustopher Jones and Mungo-Rumpel. Act Two, in contrast, is perhaps much more serious. After Moments of Happiness we meet Gus in his old age, as an embodiment of the underclass, and Skimbleshanks as an embodiment of the working-class. The Growltiger sequence also deals with the serious themes of revenge and death. There is also some kind of danger when the Macavity threat reveals itself. And even the Journey to the Heaviside adds to the serious air of the scene.

[Alonza0]

You make an interesting point. I noticed the symmetry of Jenny's and Skimble's songs before, but I never thought to put it into words. Good sleuthing. I have one point though - why is Gus representative of the underclass? I picture him as being of the upperclass for several reasons. One, his association with theatre. One typically links going to the theatre with wealth, and actors share in the profit as well. Two, if Gus is anywhere near as good as he says he is, he's likely to be one of the more profitable actors. Three, a cat of his age is likely well cared for, as many poorly-cared for creatures don't live as long as their well-cared for counterparts. A well-cared for cat is argueably a well-off one. (I'm assuming that Grizabella only survived as long as she did because of her desire to make ammends with the Jellicles.) I'm curious to see what your reasoning was on assuming Gus was underclass. Maybe you saw something I overlooked.

[Flitterbug]

Actors on stage have never been very well paid. Especially not during the time period that Gus was on stage (presumably when the poems were first written). There's also the mentions of his club "at the back of the neighbouring pub" - a cat from a higher caste probably wouldn't hang out out the back of pubs; And the "his name was quite famous, he says, in his time", which implies that he may be exaggerating the tales of his glory days...

[Vice]

[Moongewl]

Technically Grizabella ascends to someplace. We don't see her die, nor is it specifically stated that death is essential to the "rebirthing" process. For all we know, Grizabella actually goes to a third-floor apartment where a loving family lives and will take care of her, giving her a new life as a housecat.
However, nitpickery aside, I do agree that Grizabella and Victoria are supposed to represent antithetical points in life. Grizabella is age, experience, and despair, while Victoria is youth, innocence, and hope.

Even the titles of the acts suggest their different sides. Act One is "When Cats are Maddened by the Midnight Dance," suggesting eager wildness and energy. Act Two is "Why Will the Summer Day Delay--When Will Time Flow Away," which sounds much more hopeless and tired...rather like Griz, actually. They mostly bring out the less respected/popular characters in the second act as well: compare Jenny(the matron of the tribe) to Skimbleshanks(the guy who comes round for a visit when he's in town), Bustopher to Gus, Mungojerrie and Rumpleteazer to Macavity, and the Rum Tum Tugger to Mistoffolees.