Ultra Low Bass Sub?

[Yeha-Noha]

Hey guys, I'm thinking about getting a new 12" sub woofer driver for my DIY sub that I built about ten years ago to extend the ultra low bass (ULB) in my current setup. Right now it's just sitting in my living room doing nothing (see pic Smokey and the sub in my gallery). What I plan to do is add a third sub woofer to use with my dual PA 120 subs. Those have an f3 at 24 Hz. Thus the ULB sub will overlap the PA 120s a little but not their entire range. The LP crossover will be at 30 Hz. That's why I'm calling it an ULB sub to distinguish it from my main pair of subwoofers. The range above 30 HZ however is pretty smooth and well covered by the PA 120s. The ULB sub will handle just the lower octave from 15 Hz (f10) to 30 Hz.

What I don't know is will it be worth the expense ($170 for the driver) and the tiny bit of effort (cutting a 4.25" diameter hole in the front baffle for the port)?

Any thoughts?