Should there even be buff spells?
I don't mean "should we call them 'buffs'?" Because obviously we shouldn't. It sounds like idiot jargon, like "tank" or "dps".
But should there be spells whose sole purpose is to provide a bonus on some activity?
In the original booklets, there is no Strength spell. The spell to increase your strength is either polymorph or maybe growth. In other words, you increase your size or transform into something with a larger size. Similarly, there's no spell to increase intelligence, wisdom, or agility, and instead of increasing charisma or health, there are spells to charm a person or heal wounds. With one exception, the only way to improve your basic ability is to change something that improves the ability as a consequence. This actually feels right, more like the magic of legends, fairy tales and older works of fantasy. The one exception is Bless, which provides a general bonus; as a consequence, Bless always felt a little off, but since legends, fairy tales, and fantasy are full of blessings, I put up with the incongruity, although really I'd like to find a better mechanic.
In the Greyhawk supplement, we get the Strength spell. It's a lower level than Polymorph and doesn't involve any explanation of where the strength comes from. Plus, it literally increases the Strength stat, rather than making the character stronger in the game world; so not only does the spell feel very meta, but also in some cases the spell has no real effect (casting the spell on a thief with Strength 9 means no effect 75% of the time.) And on top of this, it last much longer than the traditional polymorph method. It seems to me that, if you are going to allow raw buff of ability scores, buff spells shouldn't be better than polymorphing into a strong or fast creature.
Later editions added more buff spells for every number on the character sheet to fill out the "gaps", and gave them names like "Bull's Serum". Needless to say, I'm not all that happy with these spells.