I have a large library of AAC encoded music, mostly in 128 AAC VBR and 160 AAC VBR. My plan is to bump up the CDs I import now into 192 AAC VBR primarily because I understand that, at this level of encoding, the music should be transparent when comparing it to the source disc. I haven't run the comparisons myself as of yet. What is the general consensus on the level of AAC VBR encoding that is transparent to the source material? I've heard it generally falls between 160 and 192 AAC VBR but would like to hear from you.

I just purchased an additional external drive to which I will be importing my CDs into WMA lossless. Is there anything that gets "lost in tranlation" when importing from this format into Itunes at, say, 192 AAC VBR, vs importing from the original CD? Is there any difference on how Itunes handles the WMA lossless files vs. Apple lossless?

For AAC you should ABX and see what sounds best to you. But if you want a safe bitrate without abxing 192 AAC VBR should good enough.You won't lose anything transcoding from lossless to lossy. If I where to use iTunes I'd stick with ALAC for lossless. I'm not sure but iTunes can't playback WMA lossless.