You will be MUCH better off returning when you arrive in Dublin than paying for a car each day and its parking when you won't be using it. Dublin is very walkable and easy to get around via public transportation.
And you don't necessarily need to return it to the airport location, there are agencies that have rental offices in the city as well which may be more convenient to where you are staying.Edited: 24 August 2021, 22:35
You just need to work out where you can 'dump' the car when you arrive in Dublin (as that may be in the airport itself) as you might have to get from the airport to your accommodation ..... and back again.
This might be dependent on where you are staying and which is the best/cheapest way to travel to/from the airport.
Thinking about staying Stauntons ior Buswells.
Sixt has a location in city center.
Good stuff, hopefully that works out for you.