Well if I take a 1H chart (from the SB account I happen to be using at the time) of cable and zoom it out to the max, I can see (with 20/20 hindsight, naturally), that if you'd just "sold and hold" on 11th Sept (there's a date for you...my birthday
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) until the 27th Sept, you could have made about 900 pips.
If you had sold the intervening rallies in addition, even better.
If you had managed to recognise that the market had changed at that point, you could have been making say, 200-300 pips trading each leg of the range. Taking the bias to the short side would be in keeping with what is still probably the longer trend.
It's clear that long-term, we have been living in a period of overall dollar weakness, with intervening bouts of dollar strength. However overlaying that, sterling is even weaker, and that also seems to be a long-term trend.
I believe you are right - you have to adapt. The markets are Darwinian in that sense. The more you know about the "why?", then hopefully the more you will tune into the "when".
Are the kind of people who trade based on methods which are in vogue in the forums trading big enough to move the market one way or another? I doubt it. Are the people who watch the forums to see what the retail trade is getting up to big enough to move the market one way or another? Well, clearly SB firms can skew results for their own customers if they choose to, so if you are an SB customer, and using one of the methods currently in vogue on the forums, then it might be as well to try to use it as subtlely as possible.
Dirk du Toit, author of BWILC implies that the average FX broker is about as slippery as the average SB firm, so perhaps even people on DMA are not immune from this sort of thing (although those who post on T2W seem to think that they are).
However I still doubt if even the largest of the retail traders are large enough to actually move the market. From what I've read, not even Hedge Funds can do that unless they are really large (e.g. your LTCMs and your old style Soroses).
Not all the currency transactions on the real FX market are speculation. Of course you have your central banks (acting on behalf of their national governments) who can potentially be moving billions in efforts to stabilise their currency or push it in one direction or another. In doing this in general they will be acting against market forces (if the market was going the way they wanted they wouldn't bother intervening). You also have large global corporations buying currency for imports or as hedging against currency they already hold or want to hold in the future, or repatriating profits to the "home country", etc. Not to mention the IMF and the World Bank, and I am sure there are other players on the field.
So to sum up: no I don't think the sort of trading methods typically discussed on forums like this one stop working because too many people are using them. I think they may just stop working because the nature of the market changes over time, for quite independent reasons. For whatever reason, the trader clearly has to adapt to the conditions in play at the time.