Walker tech is expensive due to it mostly being experimental but has proven itself times and times again far more effective than threads. The wolverines easily counter the use of a commando who is trained to place explosives in the exact location of the legs of larger walkers and soldiers wielding anti-tank type weaponry. A walker should never go into the field on its own much like a tank shouldn't either that's just suicide.
A good tactic for urban environment is to combine infantry with the walkers to compensate for each other weaknesses, the walkers are very much capable of taking many hits, in fact they have better armor than standard tanks however as you mentioned, their mobility can easily be affected which is why field repairs should be considered at full time. As for rapid deployment, it all depends on the situation at hand and what it calls for, but I do admit that walker tech being still experimental, it would be best to use the functioning methods already established.
On a last note, sending out experimental technologies in the field isn't the brightest of ideas but sometimes it works, look at Tiberian Sun and Firestorm, it worked wonderfully. On a personal note, the series for me ended at Firestorm, C&C3 was EA's doing and not Westwood, the studio was dead to me at that point. Every single studios that have been with EA died, truly sad.