A bit late, but just noticed your post _toommm_. I'm planning on getting an Explore Wales pass for the end of September/beginning of October. My intended itinerary at the moment is:
Day One: Starting at Crewe after arriving from Edinburgh. Crewe - Shrewsbury; Shrewsbury - Pwllheli; Pwllheli - Porthmadog.
Day Two: Welsh Highland Railway, Porthmadog - Caernarfon
Day Three: Blaenau Ffestiniog Railway, Porthmadog - Blaenau Ff; Bus to Bangor
Day Four: Bangor - Llanfairpwll; Llanfairpwll - Llandudno; Llandudno - Betws-y-Coed; Betws-y-Coed - Chester; Chester - Shotton; Shotton - Wrexham; Wrexham - Shrewsbury.
Day Five: Heart of Wales Line Shrewsbury - Swansea.
Day Six: Swansea - Shrewsbury, then back up to Edinburgh.
Not sure if it maximises the coverage, but it suits and ticks the boxes I want to cover.
Brian