Well I've done it! I just got back from a gig at a coffeehouse where I performed ONLY ballads to a very mixed audience of around 40 people – and it was a success! This was the set list:

House Carpenter
John Reilly
Billy Taylor
Dumiama
Riddles Wisely Expounded
Farmer's Cursed Wife (Kellyburn's Brae version)
Two Magicians
Scarborough Fair
Geordie
Young Waters
Willie of Winsbury
Dowie Dens of Yarrow
Raggle Taggle Gypsies
Andrew Lammie
Mattie Groves
Thomas the Rhymer

It's a nice room, not too big – only a small sound system is needed. It is furnished with a mix of tables and chairs, along with armchairs and sofas – very relaxing. They serve light meals, coffee, tea and also beer and wine.    The concert lasted from 7:00 to 8:45 with no breaks, and the audience paid attention and visibly enjoyed the entire evening. I had several people come up to me afterwards to tell me they'd never heard anything like these songs before, but that they had enjoyed them immensely, and I also sold several CDs.
I gave extensive introductions for each song, sketched out the plot and put it in historical context when I could. I think that was what made it possible to keep their attention. I'm really pleased. The manager wants to have me back – he felt it went over very well.

I have been following this thread, and at times it made me a little bit nervous about this upcoming gig what with some people saying ballads just wouldn't go over any more.   But I rarely get the opportunity to focus on ballads, so I was pretty excited about it and rehearsed a lot, and also made sure I'd prepared my introductions well.   Some of the audience had only heard me at my pub gigs singing stuff like Whiskey in the Jar, but they all said they liked these "different" songs too.

I love the ballads, and it makes me feel very good when I've performed them and they've been appreciated. It was a very nice evening for me!