I was thinking about this today, because my funds are limited since I've decided to stay home with the kiddos. But I still wanted to refresh my wardrobe a bit. Without question, I know that I will be "refreshing" my wardrobe with workout gear. Part of this is practicality; I chase a toddler and get puked on, so its important to be able to move freely and wipe easily.
The other part is that I really believe that if you dress like you're a serious athlete, you'll work harder to be one. And the inverse is true. If you put on something that doesn't make you feel good - feel fast - feel strong - then you're not going to believe those things about yourself.
I'm sorry. No one feels good in loose sweat pants and the dumpy t-shirt they got in a swag bag.
You. Just. Don't.
So I am here to say: put your money where your motivation is.
As far as athletic attire (a lot of people will disagree with me here) Nike is still my jam. Sleek. Fitted. Fast. I looove Nike clothes to an unhealthy degree (not shoes - New Balance all the way.) I will also suggest Oiselle gear for runners. BUT DO YOU.
And, no, it is not superficial to care about your appearance. You are your own brand manager. Represent the you that you want to be and you're much more likely to meet your goals.