It probably shouldn't, but in the early years of MTV, 'visual art' aspect of music was just as important as the music. It was a brand new medium.
Not music video, mind you, because that had been going for decades.
But the idea of creating music with videos specifically in mind made a person's visual aesthetics a priority. It also made it possible for people with not so much talent to be popular and sell records.
A perfect example: Big Hair Bands. I've nothing against this genre, but let's face it. Cinderella, Ratt, Crue, Warrant, Poison, Night Ranger, Quiet Riot, Dokken, White Lion, Winger, Stryper, etc, etc, etc., all played simple music, just enough to get by as a band.
Oh, there were a few gunslingers to come along, but by and large, musically, hair bands contributed nothing to the progress, the evolution of music. They contributed a look and that's about it. I'm not dumping on them. They capitalized on a trend and got rich from it. And they put out some pretty decent songs, but the songwriting, for the most part, was 'let's get a six pack and party'. They didn't really do much exploring.
Of course, the grandaddy of them all was KISS, who took all the little pieces of Alice Cooper, The Dolls, Stones, Bowie, etc, etc, and multiplied it by 10.
There's no doubt KISS was born with the intention of being seen, and then heard. I doubt many people back then said "Hey, you have to come hear this band, KISS."
The difference is, KISS did this with the hoping that 150 people would come see them on Saturday night, and then pass the word on.
Hair bands of the 80s did their thing knowing millions of kids would see them on Saturday night, from 12am to 2am on Headbangers Ball.
During that same time period, though, there was 80s techno pop. That was an evolution, the offspring of bands like The Cars (one of my personal favorites). Their look was also well crafted, but their music was also new and creative.
And don't let the Kurt Cobains of the world fool you with their anti-establishment, up yours we don't care what you think about us pose. Their look and attitude were just as carefully crafted as their music, regardless of what they want you to believe. That is their way of selling records.
To answer the original question, I don't think it's as important now as it used to be, but it's still a factor. There are always going to be young, impressionable kids just discovering music, and part of that is gonna be "Hey, don't they look cool?"