Personal preference, I guess. I much prefer to have automation envelopes all in one track rather than clutter up the screen with multiple lanes.It is sometimes useful to see them overlaid like that but editing them that way sucks and toggling envelopes on and off all the time just to work with them is a total workflow killer for me.
For me, the best approach would be to overlay the envelopes in one track by default and then have an alternative view whereby they could be split for super-detailed editing if and when such is needed.