Is 'one more significance' OK?

I don't think it matters. If there are two significances, introducing the second as 'one more' or 'another/one other' conveys the same thing. also, you're counting either way. you may not be applying number values to the significances, but you're still recognizing there's more than one.

But isn't 'significance' an uncountable noun and therefore it cannot be counted. Sorry for being confused. Thanks.

a non-count noun doesn't have to be counted to be quantified

it makes perfect sense to say "one more piece of advice," even though advice is a non-count noun.

though you might not say "two arts," you can modify the sentence to convey the same thing, "two pieces of art."

with significance, the same idea applies. it's acceptable to say something like "two areas of significance."

I found this quote online. You'll see that Tolstoy refers to 'one' significance, despite significance being a non-count noun.

“There is only one significance, you are a worker.”
― Leo Tolstoy