I agree you shouldn't simply hide collectables behind pieces of scenery like tufts of grass or railings. Unless your obsessive or have a walkthrough you'll never find those. It's the sort of thing games got away with in the past but now gamers expect things to be fairer. I liked the approach in Wonderful Dizzy where you collect coins just by walking into them and none are hidden. Method 3 was used a bit as well (coins in clouds which are not easy to get to).
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My guilty secret is that I don't think I've actually fully completed any official Dizzy game, as even when I could solve all the puzzles there was at least one collectible I couldn't locate. Still don't know where the last one is for the Amiga port of Prince of Yolkfolk - it wasn't in the same place as the Spectrum one.
It was the same for me until very recently. I completed the inventory puzzle part of the game but unless I had a copy of Your Sinclair with a map there was no way I could find the collectables. (I certainly didn't have the patience to click on every piece of scenery). I've recently started replaying the Spectrum Dizzy games on emulator and, with the help of the internet, actually completed Dizzy POTY and Magicland properly -- all collectables no cheating! I intend to upload both to Speedrun.com. Eventually I'll probably complete all of them and put them all on SRC. Or at least try -- Treasure Island and Spellbound will be challenging!
I've also played the PC recreations of the original games which can be downloaded from yolkfolk.com. Same Spectrum gfx but no colour clash, basically identical to the originals.