Bob,
The speakers in the X1 are powerful enough to handle many of the senior centers and nursing homes that you will encounter, but if you desire more coverage, or just flat-out LIKE more coverage .... you'll only need a small powered speaker. The JBL eon10 is pretty good - it's light and small and has a good sound. There are others in the $200-400 range that all sound great and are very portable.
Older folks are being inundated with the music of the 1920's and they respond very well to a wide variety. They love to be entertained and you should be aware that keeping the tempos (NOT the volume) up will prouce a better result. They fall asleep if you don't keep it moving pretty good. 50's rock & roll goes over GREAT with the senior set - they love the Chuck Berry, Chubby Checker, Elvis .... anything that makes them tap their fingers of move their feet.
Don't be too concerned with the lack of attention - some of them have long, lonely days and they don't have a lot to look forward to, so even when a performer shows up - they may be half-hearted about sitting still for an hour.
Most crowds fizzle at about an hour. Anymore is overkill. I do at least 45 minutes and mostly hour shows.
Sing-a-longs are great, but don't single out any one person - make the crowd all get into it as a unit. It ties the room together more that way.
The arranger can only help you sound better - use it to enhance your own style, or not - the choice is yours, but there is NO protocal. These folks love the big bands and if you can sound convincing .... you'll bring them right back to "the day" when they were all young. These jobs are a WIN - WIN situation.
And remember - they're not "Old" people .... they are "seasoned" citizens !