The question isn't really whether lava walls are worth it, the question is whether lava walls are worth delaying TH10 to do at TH9. Others have hit it on the head. The real question is do you want zaps at TH10? If you do, then do lavas at TH9. If you don't, then don't bother doing lavas at TH9, move to TH10, and do lavas there.
My personal opinion is that you'd be better served getting heroes to 20+, all troops done, all defenses done, then move to TH10 and start upping troops, heroes, and defenses there while working on lavas.




