I'm a new Nan and I will be very hands on, I think YANBU.
I haven't seen my DD, or GD for five days, because her DP is on Paternity leave and I wanted to give them space.
All GPs have been hands on in my family, but you still have to respect the role of the parents.
I will buy stuff, but it will stay at my house, likewise if my GD wants a pet, she can have one at mine.
It is possible to develop a very special relationship with the children in your family without stepping on the toes of the parents.
I agree with you about children now a days, being bought to much.
My DD's DP is very into "contrived" fun (Disneyland etc) I will fill in the gaps with nature walk, petting zoos etc.
I think that should be the role of GP.