I have a perfectly functional ds416 but its old too. I bought a newer model as my 416 mirrors data to it. Its a backup of my backup.
The main reason i did it is support for future updates including security patches. The 416 doesnt autoipdate anymore i have to dl a seperate file and update. Im concerned how much longer it will get security patches. When it goes end of life i can easily make the newer box my main nas. Ill probably do it next year regardless.