My perspective is going to be a little different, because we never saw it when it was on TV. It was only very recently that we got the DVDs from Blockbuster and watched them one after the other, in sequence.
I think that the last couple of seasons were subject to the same phenomenon that always occurs when TV shows become extremely popular.
By the 5th season, the show had left popular waay in the dust, and become so iconic, such a convenient standard cultural reference point that I find myself using the show to make points or concepts more accessible!
But as you will have noticed with all shows that even approach such dizzying heights, (there are none that have surpassed it, to my knowledge, Friends may be close), anyway, there is a sort of, well, I call it "cartooonization" that takes place.
Whatever elements appealed most to the public, for instance on some sitcoms it will be a phrase or word or even facial expression used by a character, will transition from an occasional thing to something that is constantly repeated. If the character had slightly big hair in seasons one and two, and becomes wildly popular, you can count on that hair being a caricature of itself in season 3.
With Sex and the City, one of the things that was most evident in the last two seasons was the budget! The girls were all dressed in fancier clothes. In fact, the actor who played Steve, forgive me for not remembering his name, was quoted as saying that the budget for each girl's clothing was around $5000 per episode, while the figure for the men was $53.
So while the girls always represented a relatively affluent socio-economic group, by the fifth season, it looked like they had all suddenly come into sizeable inheritances
Also, the last two seasons, in my view, moved well into the cartoonization phase in terms of character development, though much of the changes that we saw the girls undergo were done very well, and were in fact, as realistic as I guess anything in that show was.
But I found myself yelling at Carrie a lot more the last two seasons, so I guess they were doing something right, cartoonization and all!
For a very classic and hm, cartoonized example of cartoonization currently taking place, go over to the Food Channel and note the difference between the older episodes of Paula Deen's cooking show in comparison to the new "Paula's Party!"
To return to Sex and the City, I can tell you that through every season, the thing that kept Mr Puff and I in stitches - and shoving the next DVD in and planning the show into our Lounging time, was that we both could totally identify with everything that the characters went through.
It reminded us so much of experiences of ourselves and people around us - when we were 14.