At this point, using another spacer won't hurt, give it a try. Situations like this can arise when dealing with a Uni-body car that's been involved in previous collision damage. One space, if it saves you the head ache of more alignment problems and the sheet metal is acceptable to you...go for it.
After you put the spacer in, we can start looking at the tracking issue, time to measure wheel base. Could you report back with right and left wheel base measurements and we can compare...Don't worry about camber or castor just yet, lets get the measurements and we can start making suggestions to help you out in this department. After the wheel base issue is resolved, one more problem...the alignment of the rear bumper.
Well my friend, I am so happy that your coming close to being happy...let's keep working on these issues and get a full grin on your face.
Glad to hear good results and I appreciate your patience.