I think by 1998 (Season 30), SST kind of got back on track... granted, it still wasn't like the SST of the 70s and 80s, but on that same token, it wasn't like the SST of 1993-1998 either: they fixed a number of the mistakes they made, such as getting rid of ATC, and the large number of characters that took up space, while still holding onto some who did somehow leave an impression on kids, whether it was Muppets (like Ingrid and Humphrey with Natasha) or humans (Ruthi or Tara).
Some would argue that 2002 (Season 33) would be another change for the worst, as most fans whine, gripe, and complain about the new block format and everything, but research has shown (and Caroll Spinney had confirmed) that kids responded positively to the new format, and that the kids like predictability. In my opinion, SST has had some hit and miss seasons since then: it's hard to judge Season 33 since it was the first season that experimented with the new format, but I think some seasons went over really well (34, 36, 38), but some seasons were rather disappointing (35 and especially 37 because of all the Abby hype for her to only appear in two episodes and barely a third). Season 39 brought on even more changes, but I haven't been able to see a lot of these seasons, so I can't really give an opinion of them.