Hi Hugh,
Yes it is worth learning on2. Most definately. In terms of advantages... well on1 and on2 are both wonderful, and each has there place.
On2 is my prefered style, but im not one of those people who believe it is somehow better than on1. For me it depends on the song.
Its all about emphasising the correct beats. On1 emphasises the 1st beat (or 1st and 5th in dancer speak) more than any other, this is when you take your big step. The 3rd beat is when you start the slow or long step, you are marking that probably quite strongly too.
On2 emphasises the 1st beat by starting movement in a particular direction, and the 2nd beat with your big step(hopefully not that big, we call it big just for clarity
) The first beat (or down beat), as is the case in most music is the stongest in the song.
I wont go into music theory too much. But the second beat, coincides with the slap, or stongest accent in the tumbao for congas. check this link http://www.youtube.com/watch?v=2mQ1JOOs6LE and since the congas are quite pronounced in most salsa songs, this is what makes on2 appear more musical to certain songs.
Many clubs play timba and reggaeton/salsaton, for this kind of music, on1 is probably the most appropriate. Because in my opinion these styles of music (hiphop included) emphasise the first and third beats.
Typical salsa music, and mambo tracks are suitable for both.
I try to dance on2 when possible, where the music calls for it, and where my partner is able.
In my opinion, its worth learning on2 for the experience, to make yourself more flexible, to allow you to fit to any song, any partner, and also, to help you greater understand the music and timing of instruments.
I have plans to run an on2 in the midlands in the not too distant future.
I will keep you posted.
I hope this was some help.
Take care,
Tom