Generally speaking, I can't notice a difference between a 9.8 and a 9.9. Then again, this is just with the naked eye. I also have owned 9.8's that should have been 9.6's.
Regardless, the grading system has never been and will never be perfect, hence the classic phrase, "Buy the book, not the grade.". That's sound advice, unless you plan on flipping the book for a profit.
In regards to Hulk 181, I remember several years back when people were complaining about how expensive/overpriced it was, and that the bubble would burst, and blah, blah, blah. I'm so glad I didn't listen to those people, because I've made thousands off of H181 (i just stayed away from this book in the 9.8 grade).
So, if the bubble bursts, it's several years away from happening, and it's not going to be a burst, but rather a slow leak that leads to its value deppreciation. I don't even see this happening though.
The very fact that Disney is going to be making X-Men movies for the next 10 years is all the reason one needs to hop on the Hulk 181 investment train.
Putting that aside, Wolverine isn't a character that was made popular through movies. He's one of the most iconic superheros in comic book history, and that alone will prevent a Hulk 181 bubble from ever forming.