Also, is it worth grading coins that aren't in mint-looking condition? Or are those the types of coins that can especially benefit from grading?
Any loaded coin benefits from grading IMO:
Protection from any elements, plus the grade value can help determine price for resale.
You are also less likely to deal with any counterfeits etc etc.
Grading is subjective OFC, but still - it also keeps you from peeling it a bit, since you know it's probably worth more unpeeled.
Good luck, awesome fckn coin right there!