I rode the Etape Caledonia a couple of years ago for Macmillan and raised a fair chunk of money, i’ve also ridden it another couple of times just on the regular entry. My decision to ride wasn’t taken due to the charity aspect but due to the closed roads nature of the event. It is a bit expensive but i dont grudge paying it compared to the price of other sportives.
I dont think it is strictly true about the other events mentioned that all the entry fee goes to the charity. The Trossachs Ton and Glasgow 100 are both Action Medical Research rides and to enter either you need to pay a minimum of £50 – the fees the event organisation take on that is about £30 or so. Like Macmillan Action Medical are a good charity that i’d be happy to donate to and the events are well organised (I rode the Trossachs Ton a couple of years ago) but frankly im not spending £50 on a sportive which doesnt have something a bit special to it like closed roads when there are other charity events like the Drumlanrig Tearfund challenge where all of the entry fee goes to the charity in question.
Its not like the Drumlanrig event is a basic event either – good route, great cakes, well signed, feed stations, motorcycle marshals, free photographs, parking, toilets and so on. It is really well organised and the only thing it doesnt have is chip timing (it does have manual timing)