2004 Nissan Quest Transmission Flush

The Trans fuid has turned a bit brownish. The dealer recommended a transmission fluid flush. I quess this really an exchange of fluid and not a power fllush. Cost $159 incl 15 qts of fluid. Is this preferred? It has no problems. Should they drop the pan and replace the filter too? Is there a filter? Is this different than a flush?Not sure what to do.
No fluid has ever been added or exchanged previously.
240 hp OHC v6
Would it be ok to have work done outside the dealer?