I wanted to take the train to Barcelona when I left Santiago on 27 December, but they were all fully booked for the whole of that week, so I had to take the Vueling flight, unfortunately.
I think a train would be so much nicer a way of "decompressing" after the Camino, rather than the slightly cattle-truck-like conditions on a packed Vueling flight. And the direct train from Ourense-Barca (8.42 SdC-Ourense, then 9.25am direct to Barca via Ponferrada, Leon, Zaragossa etc, arriving 21.20) goes more or less along the Francés all the way to Pamplona, so if that's the camino you walked, you'll be able to see familiar towns and landscapes flashing past.
Another advantage is that the security people at Barca airport (if you're flying on from there) don't mind you carrying walking sticks as hand luggage.