This is more of a personal preference than a right or wrong answer.
I ask it since people might get their systems used or sell off some of their library over time.
For systems that actually had a "true" pack-in title, do you absolutely have to own it?
Are there any Genesis owners who don't have either Altered Beast or a Sonic game? NES users who do not own Mario and/or Duck Hunt? 2600 users who do not have Combat? Jaguar users who are missing Cybermorph? Panasonic 3DO (FZ-1) owners who don't own Crash and Burn? Super NES gamers who don't own Mario World?
Please note I am not talking about more recent systems which come with bundles. I'm referring back to the good old days when you used to get a game in the box (and sometimes even a second controller).
You get the picture. So what do you think? Is it important to have those type of games if you own the systems? I'd be interested in hearing opinions whether you already own the systems (and the pack-in game) or not.