Sometimes we do Single Rider, sometimes not. If it's DD19 and one of us adults, we always choose single rider, but when we throw DS13 into the mix, we are less likely to do single rider because he has anxiety issues, and doesn't usually want to ride without us. When we were recently at DL, though, he did try single rider for the first time at Radiator Springs...FP return time was like 6 hours later, and the standby line was somewhere around 100 minutes. So he decided that he would try single rider (that was a big deal for him), and so DH, DS and I all got in the single rider line. We decided that I would ride first, then DS and then DH, so that DS would be waiting with one of us the whole time. In the end, we ended up in three consecutive cars and he had blast (and we only had to wait 20 minutes!), so much so that he wanted to do it again. We waited for about 20 minutes again, and DS and I ended up in different rows of the same car the second time. Now he says that he will not have any problem trying single rider in the future.
Honestly, I don't care if I'm sitting next to my family member on the ride. We can still have fund and experience it 'together' ever if we are in a different ride vehichle or a different row. And we've still waited in line together, so its not like we were isolated. But then again, we don't all stay together all day long, either.