I've actually never thought about a way to improve season four...maybe because I don't hate season four. I think the thing of it is that the season had it's really high points and then it had it's really low points. The high points and low points are different for everybody but the low points are the things I'd like to change about the season. It was an enjoyable season and some of the episodes were just sensational but there are some I'd be tempted to skip on re-watch.
Firstly, can we get rid of Beer Bad? And maybe Superstar along with it. But I'd keep Superstar if it meant I could rid the world of Beer Bad. It was diappointed frankly and just shot down the entire season. It had actually been pretty amazing before then and by Beer Bad I was cringing--unsure if it could redeem itself from that horrid fall. But I did get over it in the end and it did mean the end of Parker, which really is the only bad thing about the first few episodes.
And what about Riley? I wouldn't get rid of him completely...actually I have no idea what I would do with him. Maybe not get him involved with Buffy--find her someone else. He was never destined to be with her, it was not going to work out. He was cool when he was ordernairy or when he was the cool super-guy in Season Six but here he was just kind of painful and sometimes even whiney. They try so hard to make him the stable, normal one of Buffy's boyfriends and fail miserably. It doesn't work, it just doesn't. So don't cut him out because the Initiative storyline worked but do something to fix him and find Buffy someone else or let her live life alone for once. Since when is it all about romance?
Adam, Adam, Adam...Why were we subjected to you as a villain? I honestly have no idea what it was that made me dislike you. Maybe because you weren't scary at all and weren't likeable to make up for your lack of scary-ness. The Master was pathetic, but he was a first season villain that I could never have high hopes for. Spike, Drusilla and Angelus were all amazingly epic. Spike had a killer personality and epic lines. Drusilla could make me laugh and could actually be kind of scary sometimes and Angelus...well, scary and hilarious lines--plus a killer storyline. The Mayor was a decent villain with a likeable personality. But then Adam was introduced and it fell, he falls as bad as The Master--maybe worse. CHANGE THE VILLIAN.
But season four, as I said, had it's epic episodes, plot points and moments. Something Blue, Hush, This Years Girl/Who Are You, Fear Itself, Restless, New Moon Rising, Tara and Willow, Spike and his chip, Giles' mid-life crisis and singing, The Gentlemen. Plus way more things that I love. I wouldn't keep Willow and Oz together because it would mean me having to give up Tara and Tillow. NO WAY.
Anyways, those are my scrambled opinions.