I suppose it's better than not going to the gym so in that regard, it has value I guess. Can't say it's of interest to me even in the slightest way.
I'm probably part of the "Jock and sports culture" Terry4 recommended, and I often look at people and think to myself "You're not one of us."
To me, it doesn't matter how much you lift, how big your muscles are, or how low your body fat percentage is. It's about who came to the gym to work and who is working the hardest. Those are the people I identify with. That may be the guy benching 400lbs+, but it also could be the guy who weighs 400lbs+.
For me, the gym is therapeutic. It's a place for me to test my physical and mental limits, it's a place for me to achieve something I couldn't do the week before, and it's a place for me to take out all my stress, anger, and frustration on a big piece of iron.
I can't stand the people wearing $500 worth of Lululemon chatting for 30 minutes while the take selfies in the mirror. They're "Not one of us."
Long story short, if you need cosplay and imagination to motivate you to go to the gym, fantastic. But....don't half a** it. Be the best cosplay imagination exercise junkie you can be.