Overnight train Barcelona-Paris ROUNDTRIP- Crazy?

Agreed....with such limited time, it'll be much better to fly. But book your discount airline tickets now, because they will sell out fast, if they haven't already. :( In fact, at this late date, discount airlines may be your only option....all the reservations for that popular train are probably gone! :'(

Why waste all the time on the train...just get a cheap flight roundtrip....

Some people have trouble sleeping on trains. If that should be you, do you really want to be sleep deprived while touring Paris?

If you're willing to use out of the way airports, you can fly Ryanair for under $100/person. If you prefer using the main airports, Easyjet and Clickair both have roundtrips for under $200 per person. This will give you more time in Paris.

IMHO, yes, this is crazy. Assuming you arrive in Barcelona on 7/16, and you're flying home from Barcelona on 7/24, you just don't have enough time to do that IMHO.

You really have only 7 full days in Europe. You can't count the day you arrive (you'll be jet-lagged and disoriented), or the day you leave. The day AFTER you arrive is questionable for some people, too (takes a while for most of us to recover from the time zone change, the culture shock, language disorientation, etc.).

If you fly someplace else in the middle of this week, you lose one day getting there and another day getting back (you need to spend a good chunk of any travel day finding your hotel, checking in or out, getting lost, getting oriented, etc. - it adds up to more than you think it will), and you end up with a 5 day vacation at best. You could try the night-train gambit but I speak from experience when I say some folks do not get ANY sleep on a moving train (a miserable experience that I will not repeat). The night train trick sounds great and may work for some folks but it is not a magical way to steal an extra day and save money for everyone.

The thing that really makes your plans unrealistic IMHO is flying in and departing from the same place. If you were going open jaws (in to Barcelona and returning from Paris, or vice versa) then it might be a little more realistic. But I think you waste too much of your trip going from one place to the other (and back). If it's not too late, consider changing your flights to open jaw (and if you can do that, while you're at it, do yourself a big favor and add in a couple more days so you have a minimum of 3 full, non-travel days in both cities). These cities are worth it, and if you have a blitz trip to Europe, you could come home after being away 10 days and find that you really only had a couple days in each of these great cities, and you'll wish that you had found some way to stay in each just a bit longer.

My answer to both of your questions is yes.