I think if Agassi had won that 95 U.S Open final he would be a top 5 player all time today. He would be atleast where Nadal is considered today, and probably above. That changed everything for a few years, and he got things all back together starting in mid 99, but by then he was pretty old for a tennis player and his ability to dominate and win alot was very limited.
Pete didnt exactly own from 96-98 like he did from 93-95 either, well in 97 he did pretty much, but not really in 96 and 98, so it would have been an even better opportunity for Agassi. I think he felt with the tennis he played in 95 he deserved atleast 2 slams and the year end #1 and to do over Pete would have given his confidence and belief he could hold his head up high in the rivalry. I am sure he knows there is no way you do that to Pete every year, but he would also know he had already done it atleast once and could do it again. Failing to do it when he had played so well that year, had been so utterly dominant on regular hard courts especialy, and when he knows Pete started the year with emotional problems as well, and to have those tough losses at 3 different slams that year (especialy the Wimbledon and U.S Open ones) was just too much to overcome pyschologically I think.
He also could hav easily ended the year #1 but pretty much gave up already on it after the U.S Open, I dont think he felt like a real #1 with having 1 less slam title and 1 less slam final than Sampras.