What did amuse me was a playaround among harpers in Edinburgh a good few years back - I'd got my whistles with me and with a vocal background, can improvise descants. Heck, a decent musician should be able to extend his busking ability to cover almost anything. Anyway, suddenly there was a certain Paddy Moloney asking if he could sit in - which is, of course, how to do it. I'm then doing impro seconds to him, which worked, and we had a fine conversation on the tin. SO, the message to the Irish is that it gets boring to the top people if you always and only play the dots in a seconds book, that's just your starting point - know what the tune does and be prepared to lead it or salvage it if someone gets hopelessly lost, but ffs do something interestingly different with it.
They used to say about car driving in Belgium, lead, follow or get out of the way. The same, I think, must be said of playing in a session: you've got to losten to four things at once, where the tune's headed, what the overall sound is, what your contribution to the sound is, and what the audience is probably hearing. And be prepared to get out of the way!