Are Hearts Worth it?

Considering caster training grounds is the only other farming spot for hearts and you aren't even guaranteed a daemon spawning at all... The ~12% drop rate might not be that bad.

Definitely worth it. Even if you're not getting hearts, you're at least earning event currency.

I'd recommend farming the goddess node so you can buy the shop hearts first, then go to the expert node to gather hearts when you're done.

If 13 hearts (10 of shop+first clear reward of that node) are not enough, yes.

Farming Hearts in Caster Dailies is futile, take advantage of the event nodes the most you can (after taking the shop hearts, ofc.

If the drop rate is accurate at 11.82%, it works out 338 AP/drop, which is a lot better than anything else, but still not great. If you spent the whole week there (minus what you need to do to unlock it), I figure you could spend 6 days of AP, and on average would get 5 extra.

When Shinjuku gets released in Feb/March we WILL get a free quest that gives hearts.

But otherwise...yes. Lots of servants need hearts for ascension (even popular 3*s like David and Medea) and most 4* and 5* servants do too.

Even Mozart---the cheapest arts support in the game---requires a few hearts.

You'll want to get all 10 of them. And once you start skilling up your servants you'll they get eaten pretty fast.

the APD of caster training ground is 640 for 1 (and is accurate , trust me)
the APD of the quest of the event is 331.
math