Depends on what you're after.
7.5 is less utilitarian, has 9 speeds, and prettier parts.
7.3 has 8 speeds and a front rack mount. Both I prefer over the 7.5's offering.

Is it worth the money? Not really, unless to you the looks and an extra gear are worth $300 for ya. You certainly won't go any faster. The carbon fork is nice (but fragile, scratches can render them unsafe,) but ride quality is mostly dependent on tire size and pressure.

If you ride in the wet, the 7.3 disc looks alright.