I think it's always a great idea to participate in architecture competitions, especially when they are free. One tends to gain a lot while doing a competition. Sure, it's a lot of extra effort, but hey, it's totally worth it! You will start pushing yourself a lots the process, learn new things and widen your horizon.
Participating as a team makes it all the more fun and will help you learn working in teams and collaborating, which is highly essential today's offices.
Architecture competitions are also opportunities to let go and freak out with your design. Remember those wild ideas you had which you thought was absolutely cool, but which you didn't pursue for fear of your professor's wrath? Well, competitions are great opportunities to explore all those wild ideas, to really come up with innovative conceptual ideas without worrying about their practicality, cost and other aspects.
And, competitions will help you improve your presentation skills, both graphical and written.
So let your hair down and participate in as many competitions as possible. Don't worry about whether you win or not. Unknowingly, subconsciously, you will grow a lot in the process of an architecture competition. And, there is always the chance that your idea and design could be selected and may open up a lot of opportunities for you!
So don't think twice, go give your best shot for an architecture competition!