Who would be arguing that Dylan wasn't rich? He was a multi millionaire back in the 60's. Back when a million actually meant something.
It's always been a fact that visability is viability, and anyone who has ever had music everywhere, on radio, on television, in motion pictures, being covered by countless artists, and becomes an ICON, he is rich.

I had a friend that became "publisher of the year" many years ago, who dissapeared from the business for a few years. He had had back to back songs of the year, and was involved with a lot of writers and artists. I never knew what happened, he just was not around any more. Years later, and now this is about 15 years ago, he popped back up out of no where. I ran into him in a resturant and asked him where he had been. He said he was making more money than ever by arranging catalogue sales. He told me back then that the real money in the future would be songwriter's, particularly the famous ones, would be in catelogue sales.
That is why you see pretty much every notable writer selling their catelogues. They can't really make much from indivually and don't really want the headache of dealing with the music industry of today. So sell them, make a huge amount of money (Stevie Nicks catelogue went for about 100 million) and be out and done.
So what if your song ends up being the theme song of a douche commercial? Can't blame em.

So for any of you aspiring writers now, go get a few hits that make a couple of grand, then sell your entire catelog off for milions. Nothing to it. But make sure your songs fit the advertising products of the future. Ain't the music business fun?