I finally did the math on WONAFYT. I did one run where someone uses WONAFYT to exclusively fight equal or lower level monsters (which appears to be its intended use), but also somehow contrives to get the +1 xp bonus on every fight (very hard to set up). The other run used the more traditional strategy of fighting monsters one level higher than yourself (I had to do two 2+ fights due to a lack of high level monsters), and then summarily executing the remaining popcorn monsters at the end. Both characters cleared the dungeon of all monsters except for the boss, and then I compared their xp totals.
I decided to actually do the experiment instead of calculating to eliminate the potential for error. I simulated a perfect WONAFYT run by using a Fighter. The traditionalist was a Monk armed with an ENDISWAL preparation (to avoid getting blocked off by inappropriately leveled monsters that might have thrown things off). I then compared their xp totals.
The traditionalist won by exactly 50 xp. Fighting equal leveled monsters is just a losing proposition in the long term.
I should point out that the deck was heavily stacked against the traditionalist. It's almost impossible to actually get the bonus xp off of every monster in the dungeon using WONAFYT. Morever, fighting monsters only one level higher than yourself is an extremely conservative approach. As your character gathers equipment, powerups, and boons, he can begin to regularly handle 2-3 level disparities, and timely use of strong match ups can kick this up to 3-4. Judicious potion use can sometimes result in 5+ victories. The 50 point victory should be considered the minimum possible advantage over a WONAFYT strategy.
Of course, none of us are actually going to use WONAFYT that way. We use it to prep popcorn monsters for the endgame (it should really be called DONTWONAFYT). But I don't think that was its intended use.
I'd just as soon have the glyph removed entirely. Right now, it's not useless, but IMAWAL and WEYTWUT are hands down better at the same job, and it's primary effect is pretty much worthless.
EDIT: Further thoughts. The comparison shows just how important it is to fight the highest level monster possible. If you remove the +1 bonus from the WONAFYTer, the he loses by a whopping 104 points. If the traditionalist does more than the bare minimum effort, he can widen that gap by another 20-50 points. Furthermore, the traditionalist typically spends less resources in spite of the harder battles because he levels up every 1-2 fights, whereas the other guy needs to regenerate several times per level to keep functioning. Bonus xp is super important and is what separates beginners from intermediates.