Long term running of an Arduino (years)

Socketed chips are just fine so long as you don't remove them and reseat them a bunch of times. I have a CNC mill with chips, some of which are almost 20 years old, still working. Plenty of those chips are dip modules in sockets. Soldering chips really sucks if you ever have to remove the chip for any reason (upgrade, failure, etc)

But, it is a good idea to reduce loose connections wherever they are found.