I think that NM 98 will lose a lot of its value after the comics boom period we are currently in is over. In short, when the comic movie bubble pops. I think the book will always have a high value, for a modern key/common book, because he's developed into a pretty origianl character. Sort of the class clown of comics. I think as long as the character doesn't become a deflated, unfunny, unorigial version of himself that book will be in demand. I made a little list below of why I like the character and why I think others like him.
Opinionated reasons I think Deadpool is popular today and will stay popular:
1. He brings a lot of humor and random-ness to comics.
2. He incorporates current pop culture into his speech and stories more than any other comic character I can think of.
3. He does not represent the typical hero (or even anti-hero). I say this because he doesn't always do the right thing when it counts like most
4. The typical deadpool reader is taking a break from the serious stories of the comic world or does not enjoy the serious comic stories and characters
5. He's unpredictable, you don't really know or can't predict how he will react in any given situation
6. There seems to be more creative liscense given to the writters and the stories don't have to make sense in any serious way
7. Ben Franklins ghost