I'm not sure what catalytic converter plugged off means, but I guess you're referring to either 'gutting' the catcon or replacing it with a straight test pipe? The only way this would really increase acceleration is if it was badly choked. As for fuel consumption, the purpose of O2 sensor in catcon is to measure catalyst efficiency so theoretically removing catcon should not affect fuel consumption, however, I've heard people report that after removing catcon their fuel efficiency has gone down.
Yes, vibration in D in stopped car is generally because of engine due to poor 'health' of engine so tuning should help a bit. Having said that, it's a big inline 4 cylinder engine which generally produce vibration due to their inherent design and I've myself felt quite a bit of vibration in my CL9 and also heard many other CL7/CL9 owners complain about it. Personally I prefer to keep the car in N if I'm stopped for any length of time.