OP
'Have we reached the stage yet where there are no more 'traditional' songs left to be collected?

Here is an honest attempt to answer the question.

First of all I interpret this as having nothing to do with folk clubs or the folk revival. (Paul is talking about collecting.) Okay, this absolutely depends on your definition of 'traditional'. Presumably we are talking about the English-speaking world so this would exclude the Corridos and the plena. we are also therefore talking about modern western society. Yes these are assumptions which may be incorrect. If you are talking about the broadside ballads and art songs that make up the vast bulk of what the first revival chose to call 'folk songs' then yes we have reached that stage. If you are talking about the songs sung in the bath, the coach trip, the odd bar-room, the songs floating about in people's heads, albeit the products of Tin-pan-Alley, then no. These songs people still remember from their youth. They're not the same type of songs as those 'folk songs' because they come from a different era, but they go through similar processes. Whether anyone would want to collect them or not, well again, only time will tell. The main impetus for collecting 'folk song' was because it was felt the songs were dying out and at least the tunes hadn't been recorded. We can't give that as a reason for collecting the songs of our youth.