Lower bitrate to higher bitrate encoding?

Here's one for the audiophiles out there...

Does encoding from lower bitrates to higher bitrates actually work, in that the encoded song is truly higher fidelity than the original, lower bitrate song? I ask because in iTunes one can encode from lower to higher bitrates, and I want to encode my whole music library as 192 kbps AAC files, for a balance of quality and file size, but some songs are currently 128 kbps and others are 256 kbps. Is there any point in encoding the 128 kbps songs into 192 kbps versions?

How does the encoding technology work if one can encode upward, from a lower quality to a higher quality file? And what are the technology's limits? Does upward encoding work if the low bitrate (e.g., 128 kbps) file to be encoded as a higher bitrate file (e.g., 192 kbps) was originally an even higher bitrate (e.g., 256 kbps), because encoding as we normally do from higher to lower bitrates involves more compression than permanent loss of data, such that "compressed" data in lower bitrate files can be expanded upward back into higher bitrate/sound-quality files?

Thanks for your insights...

Maine

Nope: Encoding a low-quality file to a higher encoding level will just make the file larger and it will actually sound worse at the higher bitrate, as it'll be compressed a second time.