Again, my knowledge of the caddy is not great, but I'll give this a go. If I understand correctly, you are asking about dropping the rear bushing for the front control arm, where it attaches to the main structure? This would result in the lower control arm being lower at the rear than at the front, and having less slope down (towards the ball joint), correct?
If so, this is not a great idea, for a couple of reasons, but is probably doable, if you had to, and did it right, and checked on it periodically. I see three issues:
Least important: the change in lower control arm angle is effectively only half of the amount you drop the bushing, as long as you do only one of the two bushings. As such it is a relatively minimal change, but you may experience a little more bumpsteer tendency, and your dynamic camber behaviour may be slightly less than ideal. Neither of these is really worth worrying about for your 1/2" spacer.
More important: changing the angle of the control arm in the longitudinal plane is sometimes done with double a-arms to create or reduce anti dive (under braking) or anti squat (under acceleration). Without having really looked at your geometry (and re-read some books that I haven't looked at in 15 years) I dare not even guess what effect this might have. If there was an effect, once you factor in torquesteer, things may get a little weird. I'd class this as a try it and see kind of thing, but it may be an issue.
Most important: those lower control arms secure the spindles, which hold the wheels to the car. Any modification you make may reduce the reliability of that attachment, and therefore reduce your safety. Any type of spacer would require an alignment pin of some sort, IMHO. Simple through-bolts would not be adequate in my opinion, as the spacer would act as a washer to allow the busing to slide, flexing the through bolt side to side, possibly leading to a stress fracture (failure) of the through bolt. And (at least on my A2), when the rear lower control arm bolt breaks/falls out, the car does some really wierd torque/brake steering. Don't ask me how I know, I just know!
So to summarize, you could probably try it, but put lots of time into designing the spacer with some sort of positive location, to ensure no movement, and be sure to select top quality attachment hardware for the through bolts, or if you are trying to reuse the factory bolts, dust them with paint, tighten them to 1/2 of recommended torque, and remove them to check that you have adequate thread engagement.