Yeah, I had a projector that used to tell me my bulb was getting old after 500 hours... they eventually updated the firmware to 1k+ hours because of so many complaints as the bulbs were lasting much longer than "recommended". Like said, just keep a spare on hand and replace when needed.Bulbs are susceptible to power on hours and physical hits/vibration normally.
If its powered off its wear is not increasing by a measurable margin.
Most projectors even have a hour calculation built into the unit and recommends when to replace once it hits the rated hour usage (some bulbs last longer, some shorter ~ usually about 2-5k hours depending on the type/quality of bulb).
My $0.02 is look at your bulb usage. If it looks like your bulb is going to go 5+ years...then just don't buy one IMO. Better chance you will have access to a better PJ in that timeframe and would be better off just buying a new PJ. However, if it looks like you will burn it out in 2-3...then buy a spare. I have had my Sony PJ (fairly high end) and still have not swapped the bulb yet after nearly 8 years and it is sitll plenty bright.Thanks everyone going to buy a new bulb soon but not yet. I barely have 200 hours on my current projector.