The forum is quieter, there is no doubt about it. I posted as much over a year ago, shortly after the off topic section was added as I'd noticed a drop off in the number of new threads and responses to threads.
As I see it the forum will get quieter still. Massively increased running costs will see many current owners sell up and with plummeting values the new owners will be more likely to be less inclined to spend on and mod their cars. Why make a car that is prohibitively expensive to run even more uneconomic and prone to failure?
Is this the end of the SIDC though? I think not.
What will be left is the hardcore, committed enthusiast. Look at 22b, hardly a massive daily post count their but one of my favorite forums due to the in depth knowledge that can be found there. I've started threads there asking a question and not had any response ti it but I'd be inclined to believe it's because nobody knows the answer, not that people just can't be ar$ed to post up. I'd rather that than a long list if "I don't know but I'm sure someone will" replies.
In a nutshell -quality not quantity.