'But I do loathe the way all these miracle stories simply conspire to send the endless drumbeat message that your child will never be helped because you were not persistent enough.'
I identify with this to a very great degree. Since DS2 was 3 we have done PECS, ABA, Floortime, Hanen and biomed, (with a bit of Intensive Interaction and TEACCH thrown in at school). We haven't ever done any of these things as intensively as is often recommended and as a result I've sometimes felt very guilty that we are somehow depriving DS2 of the chance (albeit slim) of 'recovery'.
Now he is at school full-time (since last April) we have even less chance to do anything intensive with him and have to admit we now do very little beyond playing with him as much as possible and continuing with his biomed regime (which is fairly 'light' - just supplements + gf/cf diet). We still use ABA and Floortime techniques, but we're not doing anything approaching a 'programme'.
I don't think it's made the slightest bit of difference. He continues to make slow progress, faster in some things than in others. When we were doing ABA he probably had a bigger 'stored' vocabulary, but he never used it, because he only uses words to ask for things he wants, and those things are limited. If he wants something new, he adds the word for it immediately. So we work on extending his range of desires!
I do think the dietary/supplement regime has made a big difference to him though - he is much calmer, sleeps better and has better eye contact when he's on it. Even so, he can be thrown right back by a change of circumstances - atm, the whole sensory onslaught of going back to school.
I have every admiration for people who maintain full time therapy programmes. We just couldn't do it - partly because I'm not cut out for it, partly because family life suffered. It doesn't stop me having twinges of guilt every time I read about a child who has made tremendous progress as a result of one regime or another though...