There are some plugins that work really well with the MF aftertouch (Repro in particular is great). However a lot of plugins don't know what to do with the polyphonic messages. I've got a couple (Softube Modular, Alchemy) that expect Channel Pressure when they refer to "Aftertouch".
Here's a bit of Logic Scripter script you can paste into a MIDI FX Scripter plugin to (very crudely) translate Polyphonic Aftertouch to Channel Pressure, meaning you can use MF key expression in your older plugins:
function HandleMIDI(event)
{
if(event instanceof PolyPressure) {
c = new ChannelPressure();
c.value = event.value;
c.send();
} else {
event.send();
}
}