I suppose it's party material only, but there's some value in practicing ventriloquism by doing classic comedy routines. Who's on First? by Abbott and Costello comes to mind. Or the Dragnet spoof Copper Clappers with Jack Webb and Johnny Carson.
What makes certain routines great is the rhythm and patter that takes them beyond the words to being a great performance. As I keep practicing, I'm trying to work on the transition speed between my voice and a vent voice. It reminds me of learning to play chords to a song on a guitar. The trick is in how quickly and smoothly you can go from one chord to another.
And if you want a vision, think of the dummy you'd need to do Art Fern and the Tea Time Movies. It's my all time favorite from the Carson show. Although, as a matter of fact, I just can't decide which character would be me and which would be the dummy.
I can vent Art's voice, you see. And the routine does take two.