Can I paraphrase 'It's of no value, either.' into 'It's valueless, either.'?

Question

But in It's valueless, either., there is no negative, so too should be used, right?

So, It's valueless, too. is the right usage, is it?

What I want to know is whether you sometimes use It's valueless, either. in informal English?

Answer 1

The general rule is that either is used with negations, too with affirmative statements.

I love ice cream too.

I don’t like liver either.

“It is valueless” is affirmative, so yes, the right adverb is too.

It should be said, though, that this rule isn’t ironclad. (In language, what rule is?) Consider,

It has no value either.

Though “It has” is affirmative, it’s still idiomatic to use either because of the no. An alternative sentence meaning the same thing,

It doesn’t have [any] value either.”

does conform to the rule.

To answer your second question, no, “It’s X either” would not be said for any X that wasn’t of the form X = “not Y.”