Well, relevant to whom, and for what? The music, the lyrics, the guitar, the emotions, the performances? There are so many aspects to songwriting, and you cannot separate it from the records and performances in this case.
Not sure about "niche music". That's not how you sell millions of records and 10,000-seats venues, as he did on virtually every tour since STP.
His name (not only DS!) is well known even to non-music fans, casual radio audiences. And that's certainly not doen to excessive marketing ;-)
Re "men don't listen to lyrics" - I know many men who do, and some women who don't. It's maybe more a question of formal education, language skills or personal interest.
As far his relevance as a songwriter is concerned, that's difficult. We all agree that Dylan is probably the most relevant songwriter in history, but how many titles (or even songs) do people actually know? Blowin' In the Wind, and most people won't even know it's a Bob song. Same goes for Cohen, Springsteen, Lennon/McCartney, Queen and all the others.
Re quality: same problem. All of the above artists have produced absolute gems at some point in their careers, but that doesn't mean they only produced top-notch poetry all the way through. "Obladi-oblada", "I'll be your baby tonight", "We will, we will rock you"...
It's an endless story. I think the question at the end of the day is what will people (men, women and smally furry creatures from Alpha Centauri) be listening to, what songs will be remembered, in 50 or a 100 years' time? We may not be here to see it, but my guess is that there will be a few MK/DS songs, and a few songs by all the other big names. That's my hope, anyway.