To help clarify the answer tot he original question. It'* not a bad thing to replace.
First thing you want to do is ensure the bolt holes on the body where the subframe bolts up are good and solid. A subframe usually outlasts the body, but things do happen.
To replace. Get a 4x4 about 4 feet long and place it just to the driverside of the hood latch from the radiator support to the firewall. Place a block of wood etc under the front to keep it from breaking the plastic of the radiator holding plastic piece. Chain it to the motor on the driverside.
Jack and suprort the body of the car. Remove the wheels and pop the ball joints. Disconnect the sway bar end links, remove the nuts on the front and rear motor mounts. Also remove the bolt to the passenger side dogbone mount. Unbolt the power steering rack from the subframe. Locate and identify any electrical wiring attached to the subframe and remove (all I am aware of is one clip that holds the battery cable loom to the subframe). Ensure there is not a power steering cooler line attached (if so, unbolt it from the frame). At this point you can remove the subframe bolts. The frame itself is about 100lbs. Slide it out from under the car and put the new one in place. Line up your bolts and reverse the above procedure. In all it should take 1-2 hours.
00 Regal GS: All kinds of cool stuff.