It looks like the 1 series increases boot space from 330 to 360 litres as a result of the model update? Bigger than the Civic the other half has at 315 litres.
The e46 coupe is 410 litres with the saloon bigger at 440 litres. The cavernous boot of the old Mondeo I had was 500 litres. The newer E92 is 460 litres.
I take your point about the usability of the space as I regularly use the Civic to transport stuff to the tip as I just can't get it in the E46 coupe however....
1) the RWD or 4WD format reduces boot height and width normally due to the susension layout required.
2) IMHO space above the parcel shelf is only useful for transport of a single large item and I would never load above seat level without parcel shelf for a journey - in an impact or heavy braking I don't want to be whacked in the head by luggage.
If you are going for a small RWD or 4WD car you are sacrificing boot space and performance in snowy conditions in the RWD case. Also consider rear leg room as again The Civic is too small and with me in passenger seat and child seat/ child in rear I have to have my knees behind my ears to stop getting kicked in the back all journey and to make room for child.
I know you have commented how impressed you were that we both kept our 3-door, smallish sporty cars and didn't go and buy a baby bus but it isn't without major hassles. If I knew what I know now I would have bought a military spec hummer or possibly a M5! Nowadays I would have bought a Land rover defender v8 auto complete with built in "wet room" to easily mop up any vomit, urine, faeces or mulched grapes and give me a spare hand to throw more food in the little ones direction to shut the bugger up enough to concentrate on the road. My only alternative at present is to drive as fast as possible to shorten the journey time and scare her enough into silence. In fact a black cab with bullit proof separating glass screen and already covered in vomit etc is another alternative that is worth considering for a couple of years at least.
The other alternative is to buy an Elise and a 5-series x-drive dieseasel touring for Claire (the citroen synergie also looks almost identicle and a second favourite if you could push the boat out to a Tesla?)
HTH
I agree with leather seats - vinyl would also be as easy to wipe clean.