Is it even worth mentioning your theater activities in detail if you only did it at your high school and not aiming for theater major?
If you spend time on it, theater can certainly be mentioned as an EC activity.
sure…it can not hurt mentioning it.
Yes, it is worth mentioning.
Absolutely. I did the same thing with Marching/Concert band. It shows you have passion regardless of if you want to quit.
In HS my S won a regional performing artist award and was very involved in theatre. He is not majoring in theatre (and never planned to) but has done a few college productions. He created a website with information about his performing arts background and submitted the website link as a supplemental item with his college applications. We were able to track how many views it had (no one else had been given the link) and it was viewed by multiple people during the admissions timeframe. He got in ED to his top choice.