Good question! If Ari were asked this, she'd say she's not materialistic. Of course it's more complicated than that. Her family were extremely rich and she grew up with everything she could want and that was just normal. She rejected that when she ran off to join the spacer military, and part of that rebellion was taking the attitude that material things don't matter, and that she can get by on very little. It was also practical - there's not much room on a starship and her cabin when she started her training was a glorified cupboard with a fold-up bed in it, so she didn't have room for much at all. She's still quite minimalist.

However, because of her background, she has absolutely no problem with other people owning vast amounts of extravagant things. She might call it wasteful, but there's no real moral judgement there. She also has an insistence on quality, in that she doesn't own much, but she'll only buy the very best, expensive things. The classic example is with her wardrobe - it'd be really easy to think she just doesn't care, she wears that uniform every day - but it's all very expensively tailored, quality fabrics, and she takes very good care of it (hear her grumbling in the laundry about how archaic and annoying Earth-style ironing is ;) ).

I think she's more sentimental about material things here, too, particularly anything she gets from home, whereas she wouldn't have cared that much before.