Wow, what a great discussion. As one who taught music as well as loves music, the conclusion I come to is really on context. Pete, you mentioned how if you want to play a boogie you will use certain riffs from that genre. I think that stands with all genres. There are just traditional lines we do within the genre that people have grown accustomed to hearing.

What I am discovering about music is it is as much art as it is a science. That is to say, we approach styles in a scientific fashion where we understand the chord turns and melodic riffs associated. But, then there is the art. That is where we do the unexpected. The detour, if you will. It is that surprise that rejuvenates the song when done tastefully.

My example of such an application would be the band Chicago. I had just seen them for the fourth time last week. These guys have been playing their standards for 40 years now. Yet, they have groomed their audience to accept detours when hearing them live. That has afforded them the luxury of extending an intro several minutes leading their audience in an unsuspected journey that lands up at the foot of one of their classics leaving one to wonder, how did we get here? That’s the art. I would not call it canned riffs or lines. They actually play some lines that I never thought would go over those chords. But, they make it work.

The conclusion for me is the question: what are you looking to do? If you want the audience to read a familiar part you would naturally work the conventions that are familiar to that particular genre. On the other hand, what I like to do is take those conventional phrasings and add a detour or two. It is something where the melody skirts around the chords or the typical scale run associated with the chords. The context is determined by the mood I am in.

I did not mean to hijack the conversation. This is a very good topic that has no definitive black or white answer; just a lot of neat insights for people to glean!