The graphics were better, but next to nothing actually used them (best was a basic blitter, IIRC 'Burnout' used the extras in the title sequence on the GX4000 cartridge, the rest of the game was LeMans 24 Hours direct from the old CPC). I think there were some games that made proper use of it released in France, or so I read in Amstrad Action's dying days!
My other half still has her 464 & colour monitor, in the past I've owned a 464, 6128 and 6128 Plus, I still have some 3" disks kicking around.
The Switchblade sequel I was talking of wasn't SwitchbladeII, which was never released on the CPC. It used the same clever engine (11 colours on screen in high res, the emulators still can't pull it off!), and instead of throwing knives etc you got fireballs and stuff ...