I'm not a guy, and this is a little late, but I want to put in my opinion. Dress how you want. Sure, there will be days when all you can throw on are a t-shirt and some jeans. And there isn't anything wrong with that. You can always wear a cute t-shirt and some rockin' flip-flops when it's warm. But you can also dress nicely. Go with your mood. I wear everything. There are days when I wear my favorite sweatshirt, and days when I feel a need to dress up and feel a little pretty.
As for brands, well, that just depends. First, I HATE Uggs with a passion. They are ugly. And the same with skinny jeans, which I think should have stayed in the 80's. But I DO own some high value brands, usually in purses. I've found that I can buy good, durable and nice clothing at a good price, usually things that aren't so much trendy but will be in style for years, and then buy just a few trend items to compliment. And some good shoes. But purses, ultimately, are my one weakness. I have to admit to being guilty there, as I have two Dolce, a Prada, and a Louis Vuitton. I worked my butt off for them, and they are just splurge items I had to have. But my entire closet didn't come from Neiman Marcus, either. I mix and match, pull what I like. It doesn't have to have a brand name to look good.
So go with what you feel like that day, and mix it up some. It lets people see your full personality, and that there are many facets to you.