I have a 94 Mustang GT and currently it has:

Boston Acoustics FS80 5x7 Component speakers w/ .75" tweeter in the front (150W RMS max)
A Kenwood W3005 12" Subwoofer in a sealed enclosure (350W RMS max)

The front components are powered by a PPI PC275 amp which is 2 x 75W @ 4 ohms. The sound is great, it is really clean.

The sub is powered by an Alpine T130 amp which is putting out 130W bridged.

I'm getting OK bass, but it's not really that great. I have another T130 amp laying around which I could use from a set of midbasses (i have a pair of Kicker 8" midbass drivers). Should I install those for some additional bass or should I just go with a more powerful sub amp and sub? I think the sound is lacking more midbass than low end bass.

SQ is more important than SQL for me so keep that in mind.