I guess it depends. Have you played the game you're considering buying NIB? If so, do you love it and think you're going to keep it for a long time? Can you afford a "hit" regarding value if you buy a NIB and decide you don't like it? Are you good at repairing/maintaining games?
If you've played the game you're considering buying new and you think you're going to keep it for a long time and you're not sure yet about repairing/maintaining your games then a NIB is probably the way to go.
If you don't have a lot of time on the game you're thinking about buying NIB or you're not sure if you're going to love it and don't want to take the "pay to play" hit on resale or if you're ok with doing a bit of repair maintenance, then I'd buy multiple games.
One other thing to consider is if you spend $6000 on a NIB game, will it be a while before you can afford to buy another game? No matter how good a game is, it eventually gets old when it's the only game you have. Buying more than one now will give you choices.
As all others will tell you - once you buy one, they'll multiply.