The best way around this I've found is to give to charity early in the year, and for whatever reason that somehow makes it easier to spend on myself.
How common is this? You're saying that someone, in the pursuit of frugality, begins to pursue wealth accumulation instead, and never lets go of that goal to instead take advantage of their wealth and freedom over what they choose to do with their time?
A person's preferred strategy for expending and conserving resources is an emotionally-charged choice. Who am I to say anything about their choices?
There is a certain point where one crosses into being grossly over conservative with their spending. I'm not casting any judgements of course, but when you reach that point you should probably stop and draft a will defining what should happen with your money. If you're unwilling to either spend it or give it away in life, know that it will either be spent or given away for you in death.