Your two example sentences are both correct and both mean the same thing. They’re grammatically slightly different, but the meaning is the same. By itself “Significance” and “significant” are a little different since “Significance” is a noun and “significant” is an adjective, but the basic meaning is the same. I agree with Jam, though: it seems a little strange not to say how the discovery is significant/who it’s significant to. A more natural sentence would be “the discovery is of great significance to my research” or something like that.

"The discovery of significance" doesn't seem like a complete thought. It doesn't explain... what is it of significance to? "The discovery is of significance to the _____" Fill in the blank, and it becomes a complete sentence. The Christian Community? The Hindu Community? The McDonald's Staff? To anyone who wants to have a better sex life? The discovery is significant is a complete thought.