I am sure many people will want to weigh in on this interesting question.

Re-sampling will not directly affect the quality of the RealTracks on their own.

In my opinion 24bit Audio is great especially if you are using heavy duty plugins where the algorithms will tend to work better on 24bit audio, which will give you a bit of a better result.

Or if you are heading from another program to RealBand or a recorder it makes sense to keep everything 24bit 48Khz in some cases.

some sequencers and many of the multi track recorders will render audio temporarily in a 32 bit floating point format. Before the file is output it will go through the 24 bit converters on whatever interface you might have this all allows for better multi channel mix summing and plugin operation before it gets sent to the 24bit converters in the card. Many people like to take their 24bit final mix and then use a dithering plugin as they do a final conversion to 16bit.

If plugins are not a big consideration then I would tend to suggest keeping everything in 16bit.