Hi Walker,
It really depends on what you're used to. If I did the WHW again I think i'd probably wear trail shoes/trainers (TNF Hedgehogs maybe...) and carry less stuff with me. With a 15-20kg rucksack boots are probably a good precaution since there are a few tough, uneven patches walking alongside the loch. We were lucky with the weather and didn't get muych rain so the route was fairly solid all the way. If the weather was really bad (rain/snow) I'd probably want warm boots, but if the weather stays like this... take trainers.
If you're having your stuff ferried from bunkhouse to bunkhouse, take boots AND trainers and decide what to wear on the day depending on the terrain you'll be walking on, weather, how sore your feet are, what you'll be carrying, etc.