Ask yourself: "would I self-study this material anyway if I had the next three-five years paid for? Would this occupy a large part of my time regardless of what I'm doing?" If so, it's worth it.
Philosophy makes a good hobby. You can do it anywhere, and no special equipment is required.
Doing it right, of course, likely requires having good mentors who can guide you away from the path to crankdom. Whether these mentors are best found in academic philosophy programs, I am not certain.
There are pretty strong reasons to be wary of academic philosophy. And the question here is whether there are good things to optimize for which come alongside a PHD generally, and also in particular in philosophy. So what to optimize for when pursuing a PHD?
Some alternatives include:
1) Smart students
2) Excellent advisor (with the cost of very little time and attention for you)
3) Young but still good advisor (no time-cost)
4) Level of similarity between what you want to research, and what your prospective advisor researchers
5) Freedom to do what you want in terms of directing your research
6) Confortable physical environment (Campus with sports area, good weather, and comfy social areas, nice café's to study)
7) Good contacts - Whatever that means within philosophy PHD's
8) Whatever works - meaning apply to all you can and think later, which implies that it is worth applying because it gets you a phd, not because of what it offers to you in other ways.
9) Nothing to do with academia - in this case, once you guarantee you'll get your phd, you optimize for something else, like social environment, being New York, hot students, having a beach and hiking area, etc...
Maybe some of these can be extended to pursuers of a PHD in other areas. Also, I'm assuming price is not a consideration (either all give you scholarships, or are free)
It seems to me that education is one of the things that people are most irrational about, with a lot of people going the 8 route by default, not decision, for instance. And paying the cost (in motivation, success and happiness) later down the road.