It's a gem. Only 650 Palindromes by my math, and way less VVVV ones.
Even though it isn't "Quad Premium" I like it better than most other possible sequences. I own BNNB.com so we are in elite clubs.
I would put it at $1000 minimum. Possibly much more.
definitely low x,xxx in my opinion as well. even though the U isn't premium i dont think its a bad letter at all.... possibly better than some premiums in the order that it is in anyway.... also another thing it has going for it is the visual palindrome effect as well... when its capitalized it looks the exact same forwards and backward too, which could make a nice graphic i think.... as opposed to say czzc or something which visually isnt as interesting and definitely not a visual palindrome....
If it is any reference point, I have had offers well over $1000 for BNNB.com, I know it is quad premium, but when you get to this level of rarity I am not sure how much difference that makes.
A quad vowel itself is of great value in today's market but when you add on to it the fact that it is a palindrome it's value increases two-fold. I'd say around $1500-$2000