The bit depth (read: word length) of an audio file defines its dynamic range. CDs are 16 bit, which is 96dB of dynamic range, minus a little dithering at the bottom end. 24 bit would get you 144dB, which is unusable in any audio system. Even 96dB of dynamic range is barely achievable with extremely low noise electronics in very well sound proofed rooms. This is almost certainly a moot point given that most modern recordings have about an 8dB crest (peak to average) factor.
Increasing the sample rate a little is probably a good step, but again modern AD/DA converters deal with this quite well. Properly reconstructed (read: oversampled) there should be no difference to our ears (which can barely hear past 18kHz) from an increased sample rate, and there is a much greater burden on the processing hardware. File size will also go up.
The real issue is that neither of these specifications defines audio quality. iTunes Plus did increase audio quality by doubling the bitrate of the AAC codec. I cannot hear the difference between CD and 256AAC. If I can't hear it it's unlikely than almost anyone can.