I've come across a question about the usage of "marvelous".

Actually, some of the major English-Japanese dictionaries have different opinions on the usage of "marvelous":

In a dictionary, a sentence "It is marvelous for you to do such a thing." is referred to, meaning "It is marvelous that you (should) do such a thing."

On the other hand, in another dictionary, "It is marvelous of you to volunteer your time." is mentioned.

I've been wondering what difference it would make whether you use "for" to introduce the notional subject "you" or you use "of" to do so.

I'm in terrible need of a reasonable explanation for this matter.
I'd really appreciate if you could give me any advice.

Thank you
You are worried about a tempest in a teapot, Ryujiro. There is no significant difference-- as you can see from the perfectly good sentences in each of your dictionaries.