I've been absent for a bit now, but back for at least a while.
I too, rarely use walls in PvP (whenever I play one) mainly because they take time to plan that could be used more... usefully.
By the time the walls would even come into effect they would be made obsolete by long range weapons. (on both sides)
I have found (being the turtling man I am) that a good defense using -for everyone except Cybran, T1 and T2 PDs and also T2 artilliary in a close space is effective. (for cybrans the T2 PD is accurate enough to not need the T1s anymore) A good solid line will have overlapping shield generators, each protecting another while and having the threshold be close to the front of your turret line. hopefully the artilliary will soften them up before they get in range of your main defenses. But that's just me.
Sorry about all that, but I haven't talked SupCom in a while and I guess I went on a bit.
Hopefully I'll keep in touch more than I have been. (other distractions and such)
And now I'm done talking... really.