All your posts are dead-on in this thread. People don't realize that scarcity creates demand. I know it's an accepted thing to say "If you go away for 6 months or a year, folks will forget you" but there's absolutely NO proof of that.
It's the reason every Kanye or Drake album is an event. It's the reason an Andre 3000 or Jay-Z guest verse is an event. Because they're rationing out what they feed the public. A Gucci Mane, Yo Gotti, Meek Mill, even a Ross, Wayne, or TI mixtape don't really cause huge waves these days because they're overfeeding the public/streets... Folks are like "no more, let me digest this last meal first!"
That doesn't mean disappear for 5 years, but you don't see the same level of degradation of sales numbers in genres where people don't give their music away for free. shyt, even seemingly washed up or

R&B artists like TGT and Jaheim do better numbers than most of these rappers when they drop because they ain't putting their shyt out for free.
That being said, I agree that NEW artists NEED to first offer their music for free, so that there are absolutely no barriers to people discovering/hearing their music... But once they get signed OR even just get a huge buzz after their first free album/mixtape, it needs to be paid-for albums only (Anyone can put an album on iTunes, etc without a label).
The producers of the product need to retrain the consumer to think that their work is worth something. Folks that are going to pirate will pirate, and that's fine, but at least you're not telling them that you're just giving it to them and the work is not worth anything to you.
In off-years and in between albums, artists (rappers) should just focus on features and dropping a single or two that isn't attached to any album/project, but keeps them present on radio/clubs/streets and allows them to maintain their fan-base and continue to make money performing.
This would only work if everybody(artists) bought into it though.
Mixtapes are mainly beneficial for:
Introducing brand new or unsigned artists
Discovering new producers (but on the flip-side it devalues what hip-hop producers get paid and IMO devalues "hip-hop beats" in general)
Putting out songs with samples that are too expensive to clear
Just my 2 cents.