'Overkill' is subjective. Thats for you to decide for your particular case. Performance-wise I doubt you'd notice any difference.
There are some possible benefits of doing something like this. For example, you can embed query profiling and application logging into the class. And, as you point out, you have the option of structuring the queries in a way thats easiest for you to work with and maintain.
On the other hand, the code will be less portable if it relies on your wrapper class. You cant then take that code and use it with code that relies on PDO. You might get around some of those limitations by extending the PDO class, rather than creating a wrapper for it.
