TO cater to the older and bolder crowd:
1. Be sure to use a larger TV/screen so they can see it. Having them squinting at a 13" TV isn't going to cut it.
2. Check your music selection for songs that will attract them. Frank is always a big hit, but also consider Louis Armstrong, Tennessee Ernie Ford, Roger Miller, Dean Miller (actually, the entire Rat Pack), Rogers and Hammerestein, etc. Remember, Sweet Home Alabama and Freebird might be big hits at the local tavern but not too enticing for an older crowd.
If you think your music selection is a little low I'd consider getting the Reminiscing Series or Reminiscing Gold Series from SoundChoice (I'm sure one of the sponsors can order it for you). These discs have larger type, and are mostly older songs. They were designed to be used by "independent older adults".
As for placing 'ringers' in the crowd, if they were singing songs that they normally danced to it would likely entice them to sing. You have to be careful that they sing as well otherwise you could end up with the Frank Sinatra/Dean Martin sound-alike doing tunes all night with them dancing. Try starting with a common song with everyone singing. Something like 'Down by the old mill stream' while walking around w/ a cordless having different people sing into it. Starting with a song they're comfortable with always helps.
I'd probably shy away from a 'stage'. Maybe a dias no more than 6-8" high w/ 1-2 steps (low-risers) or a short ramp if you do. Creating a space apart from the 'crowd' is usually enough if they're mostly sitting down.
BTW, how many people are you talking about? 150? 250? 500? more? The size of the crowd would dictate a number of other considerations regarding setup.
EDIT: er, uh, Lonman replied while I was typing this reply. Wasn't trying to beat a dead horse with the reminescing series thing.