Mustang Sally
Angels
Man, I feel like a woman
Deeply Dippy
Bleed
Brown Eyed Girl
And no, I don't go to a lot of parties, either.
Especially not parties involving singing.
But good luck :D
Roo
Some genuinely nice choices there Roo !  :D   When I was  playing in a Blues Brothers / Commitments style covers band, Mustang Sally was always 
great for the 'Ask a member of audience to join the singers' choice - and 'Brown Eyed girl'  very popular.  ( I hardly dare mention it Roo, but those two also sounded 
great played on a Telecaster - through a Laney or  Fender amp ; so forgive me, for I have sinned  :) )
Can I add the cliche ridden , but show stopping obvious, that our Bassist used to do as a solo acoustic guitar number - and that is 'American Pie' ?  Most folks ( almost ) knew the words - and the accelerating tempo-from sentimental to ballsy worked the audience well. 
( * Edit : I see that 38th has already beaten me to that one !  :D * ) 
  Eric Clapton's 'Wonderful Tonight' tended to go down well too, amongst (roughly ) the same age group. 
Other than that , I would recommend you consider odds and ends from the  Blues Brothers / Commitments back catalogue, as that stuff went down a storm at ( mixed aged ) Corporate and Wedding bookings .   I may be 
way off the mark beyond Roo's own excellent initial ideas, because like our own Dear PhillyQ, I'm more of a (Dinner) party animal, on the rare occassions that I am seen outside of my lair.   
Solo Guitar Jazz Standards anyone ?   :lol: