Like many others, I voted for no changes to the Great Wall. I've never built it during Civ III, and rarely build walls, either.
If you're interested in other ways to improve the Great Wall (again, not that I'd like to see it changed in GOTM, but simply for the discussion), here's two ideas that occured to me:
1.) No other civ can enter your Cultural Radius without first declaring war. This would avoid those 'nuisance' ai units that seem to have nothing better to do than wander around your territory. You can block them off with your units, tell their leaders to remove them or declare war (which sours their mood to you), or let them wander and hope they don't decide to pillage or attack you. The revised Great Wall would act as a barrier to these units, unless the other civ makes it's intentions known by declaring war. This would also allow you to block off large tracts of undeveloped land, if the terrain and your city building allowed.
2.) Require that any force attacking a city have a bombard unit present (okay, a catapult present). While horseman, knights, etc., can still do pillaging raids, worker enslavements and attack units outside of cities, the main city assault force would be forced to travel at the catapult's slower speed. Other than planning, and requiring the construction of this unit type, this would not be a problem for a swordsman/archer rush, but it would prevent being overrun by faster units.
These were random thoughts, and I have no idea if they are implementable within Civ III's internal structure, but I think they are in-line with perceived potential benefits of having built a Great Wall.