Is the expression "do not bother" polite?

"Do not bother" is not a completely formal expression, hence I wouldn't use it while communicating with people such as my boss.
You can use it with clients though, if the manner of conversation is slightly friendly between you and them.

"Do not bother" is not really formal and I'd really not use it in written form (letter, emails, IM...) because it can even come across as rude depending on the region your client is from.

I'd use

"30 is totally fine for now, there is no need for making all 60" (short and clear) or

"30 is totally fine for now, no need to go to the trouble of making all 60" ("fluffier", coming across more as if you don't want to give her extra work)