The standalones can do well, depends a lot on the condition of the machine as well as the clientele. I've seen busy washes with nice machines make no money, and I've seen run-down washes do decent income with a plain jane unit with no bubblers or digital display.
I ran an old wash for years, and the owner had put fragrance in McCormick spice bottles in the window. The one over the cherry selection was yellow and the one over the new car was clear, so I moved the yellow one to the new car and put transmission fluid in the other and put it over the cherry. The income went up almost tenfold overnight- I never would have figured something that minor would have an effect like that.