Will never letting my display go to sleep shorten its life?
Realistically most Mavericks-capable systems with built-in displays, other than the early aluminum iMacs and Santa Rosa Core 2 MacBooks, have LED back-lighting which isn't going to noticeably dim with age or be affected by on/off cycling.

If you're driving a CRT/plasma/CCFL-LCD monitor then you have option of increasing the lifespan of the display phosphor coatings (the back-light in the case of CCFL-LCD panels), but this comes at the cost of increased stress on the driving electronics of being regularly cycled on and off.