Thanks for getting us started with our first comments on a specific walk (Macleods Maidens)!
Re: walking in trainers. I know a few people who do it; and apart from on boulder fields or scree it isn't completely impractical, though there's obviously alot more risk of ankle injury than walking in boots. Chris Townsend, who is one of the Uk's best known hikers, does loads of walking in sandals. The main problem with trainers on walks around the Highlands (apart from support) is wet feet and poor grip - but you must have found that out already
For better grip, why not try a pair of dedicated trail shoes such as Merrill's - a bit more support and better grip than standard trainers but with all the comfort
Ramasaig to Orbost is a real classic walk but fairly challenging - the going is much tougher on the Macleod's Maidens -> Ramasaig leg, with ankle-twisting heather that could be hard in trainers, and very boggy in one or two places, though the scenery is fantastic.
Whales seem to have pitched up already this year (we've seen a Sei and a Minke at Rubha Hunish - and if you want to know I usually walk there in wellies
) - so why not combine some of your suggestions and head for Waternish Point - probably you can do another walk, keep your feet dryish and see whales as well:P Quiraing is probably not that wet for trainers either.