Clearing Event Shop

You can freely skip ascension mats.

I'd say try to buy out anything that has over a 60APD and then ditch the rest

I used to be f2p all the way back from last year's Halloween event, when I started, until I realized during summer event that $80 a month is actually a tiny amount out of my paycheck (friggin gasoline is way more expensive). I'd say if your budget allows for it, assuming you aren't f2p, just get all the mats you want. Even if you run out of apples, SQ can be used to refill your AP.

That's assuming you aren't totally f2p.

If you don't have the CEs I recommend doing the Kingdom of Starfield and Crystals EX quest that drops feathers at 90%. I do the same using a support with a MLB gacha CE.

I only clear the event shop if I CAN clear the event shop.
I usually just get the mats I need and if I still have time, buy the other stuff without using apples.
So by my opinion, it's up to you if it's worth spending apples on it. If I have servants that need the mats on the shop and I don't have much time left to farm, then spending apples is worth it. I'm not about to spend apples on mats that none of my servants or servants that I'm eyeing for in the future need.