NOS Tubes: Store 'em or use 'em

Whadda ya think?

Here's what I was thinking about; eventually all the classic NOS tubes or even used old tubes are going to be gone. Sure, there's lots of 'em out there but, reality is, the NOS are becoming more and more rare by the day. Let's say I have a NOS pair of Sylvanis 6SN7W metal base tubes. If I start using them today, they might last, under normal use, what...five years? What will be the state of affairs then?? Will I ever be able to replace them? Will I have to pay significantly more than I did today?

Should I just use them sparingly on "special occasions?" Should I say, hell with it, I might die tomorrow - enjoy them while I can and deal with it in five years?

What's the concensus here?