You could try moving the tracks with the most 'heavy duty' plugins to the far left (mix window) of the session, as this supposedly allows the plugs to load in a more DSP efficient manner.
Use 'Aux Ins' with effects when you can... so you can 'send' multiple channels to a single effect, so instead of putting a delay/reverb/whatever on individual channels, 'send' the channels a single effect.
Also you could start bouncing tracks to stereo 'stems'... like a pairs of background vocals, acoustic guitars, synths or whatever would be appropriate... then you can delete (or 'make inactive'/'hide') those tracks and associated effects... This will also simplify the session considerably and make 'Mixing' easier/ more fun. Do a 'save as' first, in case you need to rebalance at some point.
Time to add the other 2 Mix cards as well!!