I take it that most of their cars aren't squishy and comfortable. However, the suspension on older Quattroportes (and possibly newer ones... but I haven't driven in the new generation of QP) is very cushy, while also rigid and sporty. After driving for a while in a P71 Crown Vic, getting back into the Mas felt like being on a waterbed.
Sorry, but comparing a Police Interceptor to another Panther platform car is not really a fair comparison. The PIs have MUCH stiffer suspension because they're actually meant to be driven at high speed and aggressively. The rear end is different from other recent Panthers to give better acceleration, but it also increases engine noise from them(a Town Car turns 1800 rpms at 70mph-a PI is probably doing 2.5K or better).
The Panther platform(in non-PI trim) was the last of its breed in terms of squishy, comfy American sedans and one with standard suspension will show you that.