There were two key elements responsible for that turnaround in the 1980's - Eddie DeBartolo and Bill Walsh.Eddie D spared no expense to make the team successful. Bill Walsh perfected an innovative offensive strategy that flouted conventional wisdom and then found the players to make it happen.
No such elements can be found in the current Niners team to effect such a dramatic turnaround.
I guess it depends on how you define "dynasty", but I don't think it lasted 20 years. The first championship was in 1981-82, the last in 1994-95. I would argue that the dynasty ended in 1989-90 season with their fourth championship, even though they won the Superbowl in 1995.
The best team of the 1990's was Dallas with Jimmy Jones, Emmitt Smith, Troy Aikman, Michael Irvin, et al. In the 90's, Dallas won three Superbowls to two each for the Niners and Broncos.
In any case, I don't believe that the current Niners have anything that would indicate a return to greatness.
LW