I have done dress themes for my daughters party as themes make it more fun to decorate and such so that would not bother me as it is most probably what the birthday child would love and i am sure if you contact them and say you would love to attend just your child isnt keen on dress up they will be fine with it..
as for the birthday list i can see both sides i understand it would seem very odd and rude to have preset gifts but as a mother of a soon to be 6 year old having everyone around this time ask what is she into, what does she like, what size is she and such i would find a pre-done list a handy idea... it may be that the child has a certain thing they are are into and never bothers with much else and rather it be a list you much buy from its more of a guide to help you know more as to what the child is in to...i am also guessing the more pricey things are ment for family members that will be attending xx