When I play out, I just play songs with vocals. When I started playing regularly at this place a couple years ago, my first show there I played my best instrumental and people talked loud all through it. Since then, I haven't played any instrumentals. When I'm at home practicing, I'll mix in some instrumentals with other songs.
My personal experience is that playing instrumentals, you're maybe putting in 1/3 the work of if you were also singing. Instead of just concentrating on your instrument, you also have to project your voice, remember the words, coordinate the singing and playing rhythms, try to get some feeling into your singing, look out at the audience, remember to sing into the microphone (not below it because you're looking at your uke fingering), etc.
I have to work at the singing. About 20 years ago, I got a voice lesson from someone I had a couple albums by. He put over 30 minutes of exercises onto a cassette for me, which I've now converted to my iPod. I do the exercises for a couple of nights before I'm going to play for people, and it really improves my tone and range. I still think my voice is best suited for instrumentals, but at least I can now sing well enough to get my songs across. My singing friends still don't come looking for me to provide them with harmonies.