I so want to agree with you in terms of logic - because your statements are absolutely sound and accurate.
Except...Star Wars.
Leaving aside my personal feelings about it (and even though I'm a huge fan, I couldn't care less how successful or not it is now or in the future - my Star Wars will always be my Star Wars, this is all icing to me) - Star Wars is the exception to just about every rule, across industries.
Star Wars tried to die. After 1986/87, the toys were clearanced out, the last gasp of the franchise was put to rest with the brief Saturday morning run of the Droids/Ewoks cartoons. Lucasfilm attempted to move on.
Even without new media (and countless other film series trying to be "Star Wars" to take over interest), public desire for Star Wars didn't go away - it only died because they stopped making stuff.
In 1991, the Zahn novels were released and were bestsellers. It's been 26 years since then - and every year has had bestselling Star Wars books.
In 1993, the Rebel Assault video game was released on PC, and was a revolutionary best selling game that spawned an entire series of best sellers. It's been 24 years since then, and although reviews have not always been as stellar every time, Star Wars games have remained best sellers on virtually every game platform they have appeared on. This looks to continue with the Battlefront game coming in November, which is already trending to be the best selling game of the year.
In 1995, Hasbro (who had absorbed Kenner, the original manufacturer) released their first line of "modern" Star Wars action figures. They were ugly as hell (the initial Princess Leia is not-so-affectionately still refereed to as "Monkey Leia"), terribly proportioned, and were released at a time when action figures were still aimed at kids and in their death throes due to losing their audience to computer/video games. For the last 22 years Hasbro has offered a full line of Star Wars toys which even in years without film support still are often the best selling toys of the year - not to mention accidentally spawned the entire modern "teen/adult collector" market because it was so wildly successful - and single-handedly saved the original modern-day toy kid market it originally created.
Then in 1997 the Special Edition films, controversial as they were, each were the #1 films at the box office when re-released, which was absolutely unheard of...
..anyway, you know the rest since then.
The point is (yes, I'm getting there!) - Star Wars is as evergreen as any property that has ever existed. It is the exception to rules in every industry it touches - theatrically (see above), on home video (as much as people complain about how often the films have been re-released, they break records every...single...time - no "catalog" films even compare, they sell like brand new cinema blockbusters appearing for the first time), the books and video games - which survive independently from theatrical releases unheard of for "licensed" products...it just never ends.
Disney has been really smart with Star Wars. One film a year is not at all unreasonable in today's climate. Books, toys, and games have been coming out reliably and been respective best sellers in their areas for more than two decades straight now. Because of the tie-in to the films, it's becoming more obvious to non-fans, so it seems like overload - but this stuff has always been there, and the actual volume of product hasn't really increased that much - just even more people buying it now, on top of the already evergreen numbers Star Wars has always gotten that alone would make it the biggest IP of all time.
Any other IP, I would be agreeing with you with every intellectual bone in my body. Everything burns out, right? But not Star Wars - it's only been back theatrically for two films, and families are already making it a tradition to go see the new Star Wars film during the holidays together. It widely appeals across pretty much all demographics - not many films have five year-olds to sixty-five year olds, and all age groups in between, in the theaters together these days.
Does everyone love Star Wars? No. But I would say that when you account for everyone, from the merely mildly interested all the way to the die-hard, lifetime fans, you've captured more of the audience out there consuming media, one way or another, than any other franchise out there has - or even has potential - to do. And by several margins in many areas. Even if that "mass" effect dies down, Star Wars is still the smartest bet out there, because even at it's "low" it's still the only true gold-star brand that exists, now well into it's fifth decade.