Just how much do you spend on tubes per year on average ?

I haven’t had to replace any tube for wearing out in 15 years or so.  The only tubes I had to replace were two rectifiers in the power supply of my phono stage that were wrecked by a shelf falling on them.  The power supply runs two 300B’s as rectifiers.  

larryi, that's great, and they say that tube equipment is expensive to maintain.

My Linear Tube Audio MicroZOTL preamp is easy on tubes. I've spent a fair bit on tube rolling, but not because they wore out.  

I recently bought a conrad-johnson Premier 11A amplifier for a second system. I have no idea how quickly those will need replaced.  This system probably won't get used a lot. 

I have 50 tubes across my system and have replaced zero.  My system is on more than off.  Sometimes I keep it on for weeks at a time.  Don't let tube replacement intervals prevent you from buying tube components.  

If the system wont get used much, then you may never need to replace them.  

A lot depends on type of tubes employed and how hard the tubes are driven.  My system happens to use tube types known for long life and my amps don’t push the output tubes at all.  This is VERY important as some of these tubes are quite expensive.