When recording on location dialogue, does the difference between 24 bit and 16 bit really make a difference?

Generally, no. There are few environments (or video recorders) that will offer you a 16 or 12 bit noise floor. Many audio circuits are listed as 16-bit resolution, but that's usually just the resolution and not even the signal/noise ratio of the A/D converter. 24-bits is useful when adjusted for headroom as any footroom will be below the ambient and circuit noise floor.

Gints is on the ball as usual, very good advice and info IMO

in lamens terms and in a practical sense, there really is no benefit to using a higher bitrate that 16bit 48kz as your final output (DVD??) wont go higher than that....

UNLESS you rintending on creating DVDAudio which is a different ketle of fish, but for basic work and a good clear rate which can be up or downsampled, 16bit is fine.

as mentioned, its only the resolution.
Obviously the higher it is the better the sound quality, just remember though that most DVD players only go up to 16bit.. so anything higher is pretty redundant at this time.