>So let's say, on the same thread, someone was extremely helpful across the span of the replies to me. Let's say there were about 30 replies or so. Is it wrong of me to mark all of the replies as helpful, and then 1 reply as the solution, even though they are for the same person?

I never saw a situation where they were 30 helpful replies. However, if there is and if that has helped you to proceed step by step, than I would say yes, you can mark all related messages. Usually, we have a solution and a few helpful messages in such a situation.