What will it be like in Barcelona at 12:35 a.m. if we take a midnight flight into the city during the middle of the week? Will we be able to get to our hotel, etc OK? We've never been there.
The city should still be pretty active. One of the two 'Aerobus' express routes will take you right downtown to Placa Catalunya, where you can catch a cab to your hotel. The last Aerobus from Terminal 1 (the new terminal) is at 1:05 a.m......the second route from Terminal 2, leaves 2C (after visiting A and B), at 1 a.m. 4 - 5 Euro each..the higher price from the new Terminal 1. I don't think they have a ticket machine outside T1 yet, so you buy from the driver. Outside T2A, B, and C, the stop is at the ticket machine (you'll probably see the bus sitting there), but if it's broken (and it always seems to be when I try it) you can buy from the driver.
There is an all-night city bus (route N17) that circles from T1 to T2A and T2C and buses run down to Placa Catalunya every 20 minutes or so. But it is a slow run. I think the ticket price is about 1.5 Euro.
Taxiing right from the airport at that hour to most spots in downtown Barcelona will probably cost 35-40 Euro all in.
Sorry if this is too obvious, but make sure the hotel knows you will be arriving that late, and either has a staffed reception or can give you a door code. You don't want to arrive in Barcelona in the small hours and find you can't get into the hotel, or that they've assumed you aren't going to turn up and sold your room to someone else.