replacing baby stuff for subsequent babies esp car seats

[monkey]

I have wondered about if I need to replace things for new baby - admittedly itching to just buy something for 'it' just for the sake of it.

Car seat - now been used for 2 babies. Still unbelievably clean - looks immaculate, BUT worried it might be dodgy - possible done badly in tests, but mumsnet reviews not working & can't find this one in safetly tests - bebe confort elios ( old one - 'bout mid 1999) - anyone know?

Matress for cot - again seems fine, but now used for 2 babies, almost consecutively since mid 1999 to date.

General question - is it silly extravagance, or do people generally buy new stuff for new baby, of just make do with presents & hand-me-downs?

Well it didn't even occur to me to get a new mattress for ds2 as it was in excellent condition,and as he's now about to move to a bed, I guess it's too late.
BTW both ds1 and ds2 slept with us until they were several months old, and we certainly didn't get a new mattress for our bed.