I have spoken to quite a few top players on the subject of shaft wear (not specifically the 314). All have reported that they believe that continuous use of the cue will inevitably result in a change in the way the shaft plays (micro-fractures in the substance of the wood). That is not necessarily "bad", just "different."
If the shaft remains straight and you like the way it feels, by all means continue with it as long as you like. To refine your preference, get a new shaft, and compare the hit to the old shaft. If they feel the same, you have life in it; if you prefer the probably crisper hit of the newer shaft then switch. Simple.
Personally, even if I had a Balabushka, I would want a new shaft on it every few years (depending on use). Even at my level, I can tell a definite difference in the 314 shafts after 2 or 3 years of use (depending on amount of play, not length of time). My instructor feels the same about his solid maple shafts.