If the amplifiers in a stereo chassis share a common ground at the speaker terminals, you will most definitely hear an improvement in dimension by running monoblocks.
This is due to the fact that certain information will be canceled at the speaker due to the common ground seen in a lot of monoblock amps.
The other advantages have already been discussed. If you run long speaker cables there will be a loss in resolution compared to running long interconnects. A lot depends on how you set up your system in this regard! In general though if your speaker cable is much over a meter or so in length you will be leaving some system resolution on the table.
George's comment about ground loop issues is incorrect. Ground loops exist out of how the amp is wired. It is true that some amps are wired in such a way that ground loops are more likely but this has nothing to do with whether the amp is a monoblock or integrated- it has everything to do with whether or not the designer understands how to ground the equipment.