appreciate question

I am English and I believe both are right.

I'm American and both are OK with me.

I think in the second one, what you have is an elipsis leaving the 'it', or understood information, out. The first is what you'd likely see in writing, as we generally include as much information as possible and the second would probably be more of a spoken form. But we'll have to wait and see what Sue thinks 😃

Personally the second sounds wrong.

You can drop 'it' but then you can't use 'if'. Instead use a noun phrase or a verb phrase in the ing form
eg I'd appreciate your cooperation \ She'd appreciate a phone call
I'd appreciate having some cooperation \ We'd appreciate seeing you at the earliest opportunity

But then again that's just how it sounds to my ear. I agree with Mark, we need to see what Sue comes up with :-)

And Sue says ... Wow! I appreciate it 🙂

I'd go for wrong. Appreciate is a transitive verb and therefore must take an object. I think the omission of it is because of confusion with the similar I would be grateful if ...Both are treated as formulae, or "chunks" and used without thought to the meaning of the individual words. I know my students mix them up all the time ...