Here's my 10p worth...
If it's still not costing you anything then go for it. It's good practice. It keeps all the knowledge rattling around in your brain current too.
Don't expect too much. I went last April and out of 30 people only 6 got through to the interview/sim. They were all German speakers (Swiss/German/Austrian). It's not to say non-German speakers don't get through at all but I think you'd probably have to excel in all other aspects.
A note of warning on the flights. The tickets are Standby tickets. With 30 attendees, it can become a bit of a bun fight for who gets the remaining seats (if any!) We were all told to go home in the morning of the 2nd day. There were no seats available on any of the flights from Innsbruck back to Vienna until 7pm. That flight doesn't connect with any other flights to London, Barcelona, Milan etc (Destinations of the other rejectees I was with) So we all ended up making our own way home ( I bought a ticket back to Gatwick for £60 even though my car was at Heathrow.) The italians hired a car and drove to Vienna! Just keep it in mind..