Same with hyperspace tech 8, as it speeds up bombers, so you can have a formidable defense crashing fleet get there sooner.
I think it all comes down to distance... I noticed a 10 minute shave of time per Impulse Drive level between my G1 and G5 planet for small cargos, but only about 20 seconds between my planets in the same system. So if you're doing long distance missions, it pays off more than if you're hanging around a few close together systems.