Oh, no, normal maps require MORE detail to get the angle right. They are imported as two uncompressed channels, each of which costs as much as 3 compressed channels. Normal maps cost twice as much memory as standard 3-channel textures do. And if you use the alpha channel on a texture, that channel will always be uncompressed as well, so a single 4-channel texture will cost as much as 2 @ 3-channel compressed ones.
The cost of rendering textures is practically the same as solid colors because the shader’s interaction with lighting is the same. But the cost of rendering normals affects the lighting and complexity significantly more. It is a much better idea to use textures and forego normals. There are exceptions to this rule: water typically looks better with normals and a reflection or distortion and no “texture,” though the reflection is much more easily provided by a cubemap texture than anything else. Some studios use a single grayscale channel multiplied against a single color to provide the final texture color, but this is no less computationally expensive than a colorful texture.
Look at games on the Wii if you want an idea what modern-day mobile gaming should look like. Focus less on graphics and more on colors and feeling, if that’s what you’re going for.