Obvious thing to say but depends hugely on the song , with some 'less' is definitely 'more' (in terms of number of strings played or chord variations added) and others just cry out for a bit of filling out. Sometimes what you leave out is just as important as what you add in. What your right hand is doing all adds to the equation. Minors are really useful -and generally easy to play in most keys - but I agree that in general 7ths should be added with caution.