Kinsan,
There are various theories as to what causes GERD, the popular scientific theory being a ineffective lower esophageal sphincter (LES) which transiently relaxes at the wrong time causing reflux. For me, however, this is not satisfying. Why would such a large number of people have a malfunctioning LES? What is the primary cause of this muscle malfunction? This is not known, but there are various, but highly speculative, ideas such as bad posture causing nerve compression in the neck, thus causing weak transmission (or something along those lines). This may explain why obese people have a higher incidence from GERD; abdominal weight leading to postural problems.
Another explanation could be a form of dysautonomia, which can be caused by things like viral illness or physical injury.
An interesting journal article I read focussed on measuring the episodes of LES relaxation between normal and GERD sufferers. The results indicated GERD sufferers have no more relaxation episodes than normal people, but for some reason unknown to the investigators, the projection and distance of reflux was greater in GERD patients. This may indicate GERD is not caused by a malfunctioning LES, but actually a pressure problem in the stomach. This, in turn, could be caused by myriad different factors/conditions - for example, food intolerance causing excessive gas, or slow stomach emptying (gastroparesis).
Yet another type of theory, which you mentioned, is the excessive acid/lack of acid debate. Excessive acid on one hand naturally causes reflux problems, but lack of acid can apparently cause GERD aswell - acid is needed to assist in opening the lower stomach valve and emptying the stomach. Lack of acid means stomach contents are stored for a longer period encouraging reflux. This idea of slow stomach emptying (gastroparesis), which I mentioned before, is somewhat appealing - many GERD sufferers find fatty food to be a major precipitating factor for an reflux episode. It is well established fats delay stomach emptying. It should also be noted, that according to one journal article, fatty foods actually REDUCE stomach acid secretion by 25%. Therefore is probably the reason fats delay stomach emptying, and strong evidence for the hypochlorhydria theory of GERD. This may also explain why many GERD sufferers find apple cider vinegar to provide relief, as it is very acidic and might help empty the stomach contents. As to the reason people may have hypo/hyper acid secretion, there are various arguments - e.g. stress/anxiety, being deconditioned (i.e. lack of exercise), food intolerances (e.g. lactose intolerance, salicylate or amine hypersensitivity), h.pylori infection, candida infection, insufficient bile output, unbalanced diet (e.g. too much red meat, too much fat, not enough vege/fruit etc.)...The list goes on...
After reading all of this, I hope the bigger picture starts to emerge. GERD is NOT caused by one condition, which is why the medical community find it so hard to pinpoint a general solution.
To your PPI question:
From my personal experience, do not take PPI's for longer than the recommended period (which is detailed on the drug info website). PPI's are useful for helping your body to heal gastritis and esophagitus, but should not be used for the long term unless absolutely necessary. PPI's increase plasma gastrin levels over the long term, which means when you stop taking them, the excessive gastrin causes a temporary increase in acid secretion for a few days (atleast this is my theory). This is often long enough to undo the healing process. Unfortunately the VAST majority of alternative health claims (herbs etc.) are unsubstantiated and frankly a waste of time. They all work temporarily for particular people by a generalised placebo effect, but fail in the longer term (unless the underlying cause of your GERD is purely psychosomatic, in which they may be effective over a longer period). My advice is take PPI's if you have physical trauma (mucosal injury etc.) for the recommended time. Then work on measures such as posture, weight (which is doesn't sound like is an issue for you), and diet. See a dietician and try an elimination diet. You might be able to pinpoint some problematic foods, or foods which seem to help. Hope this helps, good luck, and most importantly of all: stay occupied, and lead a socially active life. Its probably the last thing you want to do but make the effort!