I guess if no one spends bitcoin they collect, it will be in vain efforts we seek and collect bitcoin.

Well, I believe that if it happens bitcoin will be something that is not useful, and will probably appear altcoin which can exceed and replace bitcoin, and when the moment comes, may bitcoin will never be used again, but I'm sure it will never come

If you are holding bitcoins then its really hard to believe that you will never spend them as bitcoin is also an form of money that should be spent like fiat money and if no one will spend their bitcoins then we will never see the higher price of bitcoins in future and it will make bitcoin a weaker currency.