[Chaos]

If it's better than doing BDPs then I definitely think they should be limited in some fashion. The main appeal of the tower shouldn't be the EXP.

....Wasn't the Firespitter challenge's grind power brought up in a much earlier Query topic?

Regardless, EXP is not the main appeal of the tower so far, just one 1st floor challenge, due to builds being able to spam Rebia in order to easily clear the fight. I'd argue that while putting Divine/Vorpal catalysts in the chests are a bit tempting, they're ultimately just a quicker way to get items that cost Legend Inks, considering that a chunk of the challenges (mainly the first floor) aren't at all difficult. Even if the Firespitter challenge was adjusted to prevent the grind power, the tower still serves as a bypass to some grinds.

A character-specific, but long-term reward (i.e. clearing it once an OOC day over a long period of time grants something like +1 Upgrade Limit or +1 Softcap to one stat) would have much stronger appeal, but that might require beefing some of the challenges up a bit.