I don't know why this gets brought up at all every so often. I mean, when I first wanted/got into DJing, the first skill I learned was mixing. I didn't really consider myself a DJ until I could mix, even if I wasn't all that great at it back then, and lacked creativity.
If you are not mixing, what are you doing besides providing the sound and music? I am with Taso, you don't see any high-end "DJs" charging $2500+ that don't mix. It just doesn't exist, period.
I literally sell my services b/c of the DJ I am, which mixing plays a big role in that, in addition to song choice, song timing, and knowing how to read a crowd (not all in that order).
DJs that cannot mix well are going to get booked less and less with today's tech and music availability. It's just too easy for most people to get an amazing music collection and some good speakers and call it a day.
It's not very hard to compete for the job when the pool consists of a DJs who are not mixing. If the client understands or appreciates the difference, it's somewhat of a no-brainer, they are not going to consider the one who does not mix. Granted, many don't even know what mixing means, but it doesn't take too much work to show them the difference, and then it clicks, followed by signing a contract