Overall reduction in brightness will prolong tube life, don't cycle it where possible, if you're going to use it on and off over the space of an hour for example, then just leave it on.
Reducing brightness will also prevent phosphor burn, where you will see ghosting of previous data/characters etc when the device is off. No way round it and nothing you can do to rectify it, just use it only when needed.
What are your plans for the terminal? I have one in the loft, I love it's 70's/80's design, it was given to me by a good (now passed on
) friend, so one day I'd like to get it working. I'd love to have it hooked up to some sort of standalone chat system, using either internet or SMS/GPRS data links. Maybe one day....