That works well if you have a group (like mine and probably yours) that always completes their careers pretty much no matter what. I want to keep my career cards, none of them really "suck" so much that they are not worth having. In fact, only people wanting the "magical careers" make any sense on cutting out early on another career, and they suffer enough to not start there
As for the rest, you are pretty much reading my mind as to what I am thinking. 15 advances to hit your next rank would be much better IMHO, and yeah, it makes rank increase a far better thing. Even if you want to go from career to career and not take "OOC skills", it places a non career based limit on what you can do.
Thinking about it a tad more, what if you tied "bonus dice" to rank as well?
You can have tons of bonus dice, as long as they come from separate sources, but you can only get one bonus dice based on the same source? This would prevent twinky fortune dice career changes, or dice based on careers as well.
In the end, you should get more rounded characters, and campaigns don't seem "ended" at around 40 advances. My fave campaigns lasted for a minimum year, and that was when I was in my teens and could play 20 hours a week and it not matter!!