A few notes:
- Gremlins and beasts are resistant to elemental damage. As a result, the damage bonus will be a big % of a very small number. Keep that in mind for the 10k bomb. :)
- Haze bombs upgrade to weapons with huge damage clouds... however, status effect damage does not receive the bonus. (according to dev comments)
- That giant status effect cloud is also much larger than the area of actual damage dealt by these bombs. Last I checked, even the 5* ash of agni will only deal direct explosion damage to monsters standing within ~1 floor tile of distance. So that damage bonus is not as stunningly useful as it would seem at first glance.

Overall, these things may impact the utility of a damage bonus in unexpected ways. Undead and constructs are weak to elemental damage, so if you have to pick a bonus, then the small % extra damage might be more useful if stacked onto a monster's inherent weakness. At least, this is as far as I've seen- if this has changed, I'd love to see more information about the new game mechanics. It's still not quite clear how big a bonus you get from doing various things.

(Sorry, NJ. Ironically, I never would have noticed this thread, had you not posted again with nothing more than the word "bump".)