Why don't you try an external wave editor that supports batch processing. Make a backup copy of your audio data, use the wav editor to change everything to the new sample rate and bit depth, change Cakewalk to use those new settings and then futz with a backed up copy of the original project file to see if you can make it happen.
Please note I have never done this, so I have no idea if it would work but there has to be an easier way than importing everything a track at a time.
CJ - You are wrong to state that there is no advantage to converting files to a higher sample rate. If you are using plugins that do not internally upsample, then using them with converted files at a higher sample rate will give better/cleaner output from those plugins.
Ciao,
Q.