Instead of thinking about what you magic can actually do, try thinking about how it actually occurs. So, let us conduct a bit of a case study here. I will use the systems from Fullmetal Alchemist and Eragon. (Say what you will about inheritance cycle, but I do like the magic system for having simple rules, yet allows for some complexity in usage.) Read the last 2 paragraphs if you don't want spoilers.
So first, Fullmetal Alchemist. Alchemy is essentially transmuting one material into another. That answers "what", pretty basic, but not very detailed. But, its the rules and workings of alchemy that gives it detail. Here are a few:
- Alchemy is done via a transmutation circle.
- The transmutation circle can be pre-drawn such as the case of Roy Mustangs gloves.
- Different circles must be drawn for different processes.
- One does not need a circle if they have seen the gate of truth.
- There must be an equivalent exchange, one cannot "create too much from too little"
- A philosopher's stone does not circumvent equivalent exchange, but rather is a source of "cost" that can be used to increase what is created, once it is used up, one can no longer "break" equivalent exchange unless a new one is acquired.
- Philosopher's stones are created from human souls, how long one lasts depends on how many souls it has. The souls get used as a substitute cost.
- A Philosopher's stone can be split into many portions so long as each portion contains at least 1 soul.
- The cost of alchemy is payed through the gate of truth which exists in every person
- One can no longer perform alchemy if they lose their gate.
- And so on and so forth...
As for Eragon, magic is a real physical effect invoked by a spell. And like a detailed magic system, it has rules:
- Spells are spoken in the ancient language.
- What is said in the language is what happens.
- Spells can be as long as need be for precision.
- Spells cost as much energy as it would have required if the effect was done manually.
- Overexerting oneself results in death.
- One can outsource energy cost to other living things.
- One can store energy in precious stones.
- Grammar is important.
So, as you can see, what gives magic detail isn't what the magic can do, but how the magic works. A good analogy is physics. What makes physics complicated isn't what it is, but is the absurd number of rules and concepts that it has, laws of physics such as Newton's laws of motion, Maxwell's equations, particle-wave duality etc. Similarly, to add detail to your magic, you could create a set of rules, the laws of magic, if you will. Once you do have a set of laws, you can then extrapolate some gimmicks the magic might have. For example, in Eragon, instead of saying "die" a magic user could say "sever his carotid artery" instead to save energy. The end result is the same, but the cost is different.
As for the races, spicing it up isn't really necessary since this is urban fantasy. One trait of the genre is that creatures that appear in myths have been living along side us all this time. But, there is a way to differentiate from high fantasy and that is to diversify your races, essentially make it less homogenized. How might orcs from different areas of the world have developed differently? This also happens to solve the region problem in my previous post, just make regional variants of existing races that somewhat match mythical descriptions. For example, you could say that Rakshasas are simply a variant of Oni. Just an idea.