valve adjustment +front and rear gaskets on 1999 Acura TL

My Acura dealer has given me a price of $576 to replace front and rear valve gaskets and to adjust the valves on my 1999 Acura TL with 91000 miles on it. Is this a fair price or a ripoff?

Asked by for the 1999 Acura TL
This seems a bit high to adjust the valves. Here is an idea of what it should cost:
For some reason they are higher, I would call around to a few other shops too. They may be including something else in the repair, make sure you have a very good understanding of what they are doing for that charge. And by the way, the valve cover gaskets are replaced as part of the valve adjustment so there is not additional charge for replacing them.
Can you please tell me why valves would need to be adjusted as opposed to merely replacing the valve cover gaskets? Thanks, I'm trying to learn everything I can because I'm tired of men assuming that beause I'm female, I won't know anything so they can tell me any little old thing they want and I'm gonna believe them, lol. Time to show them wats up!!