If you can afford it. But I would recommend upgrading the RAM first (if you haven’t already). Generally that tends to provide the most notable performance boost.
The i5 is already a quad-core, so it is more than enough for what you’re planning on using it for.
Since you reference the i5, that's means you're getting a 13" MBP. Those games are not going to run very well with the integrated gpu, the CPU upgrade will not impact performance that much.