i created these wallet.dat files on an offline machine in 2014 using QT. I've sent coins to the receiving addies over the years. these files are bip38 encrypted. do i need to do anything to these files to keep them usable and viable? if so, what? additionally, what is the argument against this form of cold storage? thanks so much.
As long as your machine remains offline and encrypted the files should be usable as long as your hard drive is.
People choose to make multiple forms of backup in part to protect against equipment failure. Paper wallets printed with appropriate paper and ink can last a very long time and can be stores in safety deposit boxes, buried in a hidden location (properly sealed of course) or hidden as words in a poem.
Hardware wallets are another option, but still will require you to store seed words in order to recover in case of equipment failure.