HI also a returner my bongo has only very recently got to the point of thinking about replacements as she is no longer repairable.
Another Bongo i thought - but what if this one also rusts/has coolant problems etc etc too (panic panic.) shouldnt i get something more recent.?
So have also been doing some research - starting with smaller now its usually just me - i found some nifty looking removable camping pods for bellingo kangoo and peugeot partner.But actually theyre a bit hefty so not so removable for me - not a lot of room for the occasions i do take a grandchild or two and although a tailgate awning is an option -it is a bit pricy when i have a perfectly usable khyam from the bongo.
So i moved up in size and found very little between mini camper and bongo.
but to answer your question found some dimensions and mpg estimates that i will pass on below.Nearest in size to the Bongo -in fact almost identical (as tin top) is the toyotta Noah which i read is the replacement for the older Regius - but re-sized. looking on sale sites i havnt spotted many and then only a couple which were 300 miles away fell in my budget range.getting around with no transport an issue -( i could potentially blow a substantial part of my budget on train fares and taxis before i find the right one)
After that.
Bongo L4.6xW1.7xH2.1 mpg 24

( which makes me question the other esitimated MPG in this report as i got a lot more than that from mine but it was unconverted out of town mainly off motorway driving and the report claimed to have averaged out those differing conditions so maybe thats the difference)
Regius L 4.75xW1.69xH1.96 MPG 27
Alphard L 4.8x W1.8xH 2.1 MPG 30
Elgrande L 4.8xW1.8xH 1.9 MPG 27
Mercedes Viano L4.8xW 1.9xH1.9 MPG 28
so not a lot between them in size Alphard is claiming better MPG though -
but those few cm longer or wider are important for me as i have to park at work and there isnt a lot of room - black looks emmit from colleagues and one complaint about the bongo (from some-one who happens to think his car is a tank and the boss knows it )- but anything bigger and they might withdraw the kind offer to let me park there permanantly which leaves me the choice of public car park.
Its not just size (I know, us girls say that to all the guys

) but i know very little about these vehicles - i knew little about bongos 12 years ago too - but since being on my own between this site and some very helpful members i have got by - I am sentimentally attached to bongo,s as well (which doesnt help me think logically) and again i have the right size awning and all the camping gear so for me, its starting to feel like actually it will probably be a Bongo.( swivelling seat is possible now i believe)
Good luck with your search though i will be watching your thread with interest.
So it more a debate over 4x4 2.5 diesel turbo /2.0 petrol /tin top/Aft .