Nope, Spike, Drusilla and Angelus together is what elevated Buffy to special status. Without the other members of the Fanged Four to plyay with Spike loses the vast majority of what made him a great character (I don't ever like Spike but I won't deny he, Dru, Angelus and Darla all sparked when they were around each other). You see, Spike....is stupid. He can't plan worth crap, gets his ass kicked over and over and over, and just plain acts stupidly for his entire existance. The sole reason Spike made it past Lover's Walk is because he was popular. The entire cast had to be dumbed down and act out of charcter to allow his continued existance, after the events of season four Spike would have lost anything that was keeping them from slaying him.
From S3 through S6 Spike dragged the show down (now, this is in no way reflection of his acting or the enjoyability of the character himself) until the Scooby Gang looks liek a bunch of stupid, incompetent, hypocrits that deserve everythign they get. This is mad eespecially bad by the fact that rather than just giving Spike a soul right away the writers allowed Spike to continue actively pursueing evil for four seasons while still interacting with the good guys. Time and again Spike proves the chip isn't preventing Spike from causing harm or aising the dark forces and the good gys just sit there and do nothing, except maybe smack him around a bit which does nothing.
Joss didn;t care about Buffy by S7, he'd gotten bored and moved on and only popped in and out when he didn't have more interesting things to do. Honetsly, Buffy the character was flat out ruined that last season. Her plan was ridiculously stupid, didn't even work and had to be saved by the Big Bads from a different show.