I would personally say no and get a more recent phone, the Xperia Play hardware does well with most emulators but I have noticed it struggles with newer Android games, even with a custom ROM. Not to mention the poor battery life as well, makes it hard to use as a phone.

Buying a phone with a bluetooth gamepad will be my advice. I have the HTC One M7 and use a Moga Pro gamepad with it, and while I find gaming on it great, I do have to admit I miss using the Xperia Play's built in gamepad. If you do plan to go this route, I suggest getting a phone with dual front facing stereo speakers, it makes the gaming experience much better.
HTC One M7 - Sense 6.0, Android 4.4.2, Stock Kernel - Active
Google Nexus 10 - Android 4.4.4, Stock Kernel - Active
Sony Ericsson Xperia PLAY - CyanogenMod 11.0, Android 4.4.4, CM 11.0 Kernel - Semi-Active