I haven't found such a thing as too friendly.  We've got an older cow that was a twin at birth, and the cutest thing you ever saw.   Wound up spiking her on a different cow so she was worked with a lot very early on.   She loves to come up to me and have her face scratched.   Even during calving she's as mellow as can be.   I'm not looking forward to the day we have to sell her, but it would bother me even more to leave her until she died and had to haul her out.

I've always considered friendly cows to be a good thing.   I can't stand hot headed animals.