Oh for sure, I think we can safely say Roger would have never won the career GS in the 90's and Nadal wouldn't have by this point in his career either, he still could if he continues to adapt his game, but I don't think he would have won it either.
Although you could make the argument that Agassi winning on all four surfaces, yet not even being the best player of his generation meant that it was a weak era. I don't believe that, but I bet that could be very well supported.
I don't think so either. If the courts from 1990-2000 were set at the same pace as today, I think Agassi would likely have grabbed a couple more Grand Slams, and may have squeaked out a couple more big matches against Pete. Pete would still have been the greatest of the generation tho, but maybe not quite as lop sided. The only evidence I can cite is Agassi's play in Australia over the course of his career, including 2 big wins against Sampras. I think we can safely say the courts at the AO were way slower that USO or W in those days, and it seemed to help Andre a lot in those matches. However, as we have learned from the Fed/Nadal match ups over the past 1/2 decade, tennis is a game of styles, and Sampras game was a match up nightmare for Agassi. The 1999 Wimbeldon was the best example. Agassi won the French and was on quite a roll getting into the final of W. Sampras took him to school that day. I am not sure anyone could have touched Sampras on that court, on that day,