Unity has a Substance engine I believe to be comparable to UE4's. If the Substance has exposed parameters you can change them, and if the material is being used as a Substance(not as baked textures from the substance, as not all platforms are supporting it yet), you can change those parameters at run-time.
I'm no artist, but I can tell you, these softwares, if you learn at the least some basics, can help you make better graphics, especially combined with pre-made textures(like GameTextures.com textures). I don't think it will help with "hand-made" textures like some cartoon styles because those require actual art skill generally, while using pre-made textures and Substance Painter you can take a UV, mask off the UVs, and apply materials that can look good if done right. But this is more skill with software, not so much with actual art. It is like making textures/graphics relying primarily on Photoshop filters instead of actually drawing things with the brushes. It CAN work though in my opinion.
About Substance Designer, I think it is also a worthy investment. In theory it allows you to not be an artist and via the node system still create good textures. I haven't done much with it, but given time I've been able to make a couple things that I wanted to.
I honestly believe the LIVE Subscription is perfect for me. The $20 per month isn't much for me, a working adult with 3 children and a wife. But I had a bit of a head start, having learned basics of modelling with Blender3d, and knowing basics of UV mapping, etc... despite not having actual artist skill.