On the other hand, if it is "broke", the long-term effects of tDCS are about as well-studied as the long-term effects of many of the psychoactive substances (legal and otherwise) that we regularly take. No one knows, e.g., what happens to brains 50 years after 5 years of chronically administering SSRIs. Nor do we really know how to characterize "the long-term effects" of nicotine intake (and it's not at all clear that the "long-term effects" of anything that changes one's brain -- apart from in obvious ways e.g. by shrinking it -- is even something that it would make sense to try to characterize).
In general, when it comes to psychoactive anything (and you might even include words, music, prolonged withdrawal from society, and sexy walking in this list) we don't have much more than a few interesting results here and there. When it comes to brains/minds/persons, we really don't know.
What we can surmise is that those things that mammalian brains have not been exposed to (LSD, tDCS, fluoxetine) are likely to have less predictable effects than things in the environment that are phylogenetically familiar (sleep, exercise, prolonged concentration, temporally extended effort, etc.).
In other words, if things are going poorly for you, try the boring approaches first. If those approaches don't work, though, there aren't really any compelling reasons to avoid techniques that are less familiar to your biology.