I think it'd be a cool catch-up mechanic to help people reach lv80. I'm definitely against increasing the exp beyond lv80 (leave it as is). Leveling has always been a long journey in PKO and is one of the reasons why I think the server has had such a long life cycle, because a ton of players weren't even max level for the longest time.
I also wouldn't consider it a spit in the face of those who worked hard to reach lv80, simply because that hard work has always come with some pretty huge benefits in PK due to the level difference damage calculations, the extra stat points, as well as the extra skill points.
It's already not really a challenge to reach lv75 at this point, whether you do it yourself or pay for it. (buying plvl makes it a matter of a few days of leveling from lv70, at most.) I feel like anyone who wants to put in any real effort to reach lv75 has already done so.
From my point of view, i'd support increasing the exp rate up to lv80, and then leaving it as is.