I have a 16 and a 10 yo, both girls. Both of whom still enjoy loads of stuff.
Nail varnish - I'm with you on that, as I think it is 'growing them up' too fast. But then I don't wear it anyway, so they have never just wanted it to 'copy Mummy'. We left it until around age 9 when they could be trusted to not spill it in their bedrooms.
Theme parks - I think it is OK for you to say you don't think they are good value for money, especially if you don't like them yourself so you are paying more just for your DD's enjoyment. But Paulton's Park near Southampton is fantastic for 3 year olds. And children under 1m high get in free, and you don't need to spend any money once you're in there. Also, there is some research (if I remember correctly) saying that children who have been to theme parks are more likely to be confident or something, as they have done slightly scary things and survived.
You have to do a lot of things before kids get bored with them. We had season tickets for about 3 years in a row for Paultons before the novelty ran out, and after a few years break I have just got them again for DD2.
We do a fair amount with ours, but both were still delighted to go to Disney Paris last year for the first time.
On the other hand, if you were talking about age appropriate films, clothes, books etc I would be right with you. I really don't get why so many parents are happy for their 7 yos to watch 12-rated films.
But you can't just make them 'wait' for everything, as things have a 'best age' and you need to do it then. e.g. Paultons isn't really designed for teenagers, it is designed mainly for 3-12.