The Spark is actually smaller in the air than the Mini, checking specs a while ago on both DJI specs pages for these aircraft.
Folded of course the Mini is smaller.
Besides Mini wind issues being so light, there is a bad uncommanded descent problem, brought on by the rear props deforming in storage most likely.
Over on MavicPilots there are a huge string of them, losses on land crashes or into water, and DJI look at logs and replace clear incidents that have this happen, even without an aircraft 'body'.
The Mini was made with one thing in mind . . . to allow travel and flight easier in countries with the sub 250g rule for drones.
With changes to some World airspaces, even the Mini sub 250g status is probably going to be a moot point in the coming year or three, and some countries bring in or lean towards having any drone with a camera requiring registration and / or licensing.
Spark seems to be so much more 'solid' in wind and every other way vs the Mini.
I shot 3 videos on Sunday coming home from Melbourne to Adelaide, the first 2 were in quite strong winds, but it handled the flights reasonably well considering.
edit typo