I think that showers are a form of social insurance...one needs to buy a bunch of stuff for a new baby all at one time. If friends/family give you a shower, then that spreads out the costs. Over time, you, too will buy gifts for other people so you will "pay it back".
So in general, one only needs that initial ramp up one time. Then you have a high chair/crib/stroller etc.
Now if you had a second marriage and the other person who maybe had a baby before, but no longer is in custody of said baby items, then it would not be an issue to have another shower. If the previous baby is 20 years old, then invite whoever you want. If the previous baby is 5 years old, then I would not reach out to that person's family as extensively.