I was denied for this same card, thinking it would be an "easier to get" Visa Signature (which I wanted for the dining and entertainment benefits). What was pretty baffling was that I saw FIA pulled my EX score, which was 749 even after their inquiry. Personal income is low (40K) but HHI high (300K).
I called and asked for a recon at which point they said I had too much credit available. FIA Card Services IMO is one of the more conservative banks in granting new credit. I've had great success with Citi, Chase and American Express.
How old is your Citibank card? They would probably give you a CLI or product change if you've had a good history with them. Although you might want to watch out for the World MC, which they like to offer people with good histories because World MCs have higher interchange rates, but there are reporting issues associated with the World card.
If you're looking for a Visa Signature product specifically, Chase Freedom approves its customers for that pretty easily (I got changed over to a Chase Freedom Visa Signature from a student card and they didn't even ask for my income or any other information, just call different reps until you get an answer you want, I hear Chase has to be dealt with that way).