I have some VTC5s that are six years old now that I'm still using. Mind you, they've only been subject to very gentle and intermittent use, but I tested them last year and they were still at ~90% of their rated 2600 mAh capacity and their internal resistance was still quite good as well. Disclaimer: None of my other cells have held up quite that well over the long term, but I'm becoming pretty confident that age alone is not a big factor.
That said, I think everyone should have some spares in stock, ready to put in service when the ones you're currently using do start ticking you off. I don't know about anyone else, but I don't want to feel pressured to find replacements; I'd rather buy them when I see a deal and have them when I need them.
I also respectfully disagree with Mooch's recommendation to constantly rotate through all of one's batteries rather that using some while keeping others in storage. For best longevity, our batteries should be stored at a 40-50% state-of-charge, not fully charged, and rotating through your entire stock mean they will all spend more time fully charged than if some of them just sat in storage.