Besides playing in a couple of bands I do a solo act with backing tracks. The backing tracks focus on jazz standards , and smooth jazz with a few pop tunes. I play a Synthophone and do some vocals.
I have had the most success playing background rather than as a featured artist at a concert, although I have done some Senior citizens homes and concert in the park things.
Variety is the thing that keeps me alive, so I am constantly looking for a bigger song list, more instrument variation and ensemble sounds. I recently bought a TC Helicon Voice Live Touch. At this point I have only done some experimentation. I can see the potential although it will probably see limited use. I think this will be a nice tool if it isn't over used. A really cool feature is it's ability to follow an MP3 that can be inputed via an aux input.That is nice because I don't play a chord instrument or have another player to input. It does a nice job of simple harmony especially 1 added voice and in some cases 2. The octaves added can fatten up a 2 part harmony very nicely too. So far I can see using this selectively to add a little spice to some songs. If it's over done than ...well it will sound overdone.

If the harmony and or effects sounds synthesized it's because they are. The trick of course is to sound as credible as possible. In the pop world today many of the vocalists use effects that sound somewhat abnormal. I'm not saying it's bad just different. So if it's tastefully done so be it. It's all a matter of personal preference. It's really the same thing I face with playing the Synthophone. I am trying to shoot for good emulations of the different instruments I play. Some I do real well while others might be questionable. Is it entirely necessary that I play a perfect Trombone or Trumpet sound?
I don't think so as long as the music is performed well generally people could care less what instrument patch you use. I could be doing a really nice flute emulation and people still can and do say "Nice Sax" . That's because they see a Saxophone and hear with their eyes. I just read your post and thought I'd throw my 2 cents worth in since I haven't posted in a long time.

www.saxmagic.net

http://www.saxmagic.net