Yeah, a guitar can indeed be used as a melody instrument in an Irish session. And there are always times when the easy distinction between melody instruments and rhythm instruments breaks down, both ways.

But I think that in general that's not what the guitar is best at doing. I think any guitarist with the skill and the taste to do it, in keeping with the music might be better to be doing it with a different instrument.

As for "flashy and obtrusive" - well that's a matter of personal taste maybe. In general I don't like it in any instrument. There's times and occasuions, but in general, no.

And the description of a guitar as "a bodhran with strings" - it's a phrase I've used from time to time for years, but the reason it came to mind just then was because at Whitby Festival Denny Bartley used exactly that phrase in a workshop.