Dave, I did not see the ad until you mentioned it (then I found it on page 88).
The trouble with those ads is that they are all grouped at the end of the magazine, after all the editorial content. So, once I am done reading the content part, I am usually done with that issue, i.e., I just skip the end of the magazine where all the ads are. Just like I fast-forward ads on Netflix and Hulu, btw. But, that's just me. You wouldn't know, of course, until you try. That's the only way to ultimately see how many responses you'd get.
Now, may I critique your ad, please? Yes?... Thank you.
Had I went through ad pages, I would have probably just skimmed through and ultimately skipped your ad. On the positive side, it is yellow, thus practically jumping off the page. On the negative side, the most prominent part of the ad are the words "Photography.info." Now, remember, my glance and my attention span for that ad are rather fractions of a second, thus my reaction would be: "I do not need any info on photography," and move on. After all, I am already reading a photographic magazine to get the info.
What I think you should emphasize instead is "Isle of Skye" and perhaps "Scotland." If anyone would be interested in attending your workshop, they would be precisely because they are familiar with those names (in terms of landscape photography locations). That is the main attraction and the reason to come to you. Among landscape photographers, Isle of Skye has a legendary status world wide. I mean, I've known it for at least the last fifteen to twenty years. Back in the late 90s, I flew from Moscow to Cornwall for a workshop (with Joe Cornish) because I already knew about Cornwall reputation as a landscape location. I would have preferred Skye, had there been a workshop there though.
Next: picture. I know it is predominantly a financial consideration, and you did the right thing by testing the water first, just to see if there is any interest that way, but for me THE ONLY WAY that would make me look at the ad longer than a split second, would be a picture. And not any picture, it would have to be a stop-me-in-my-tracks picture (which, luckily, wouldn't be too hard for you). I want a picture that would make me drool and say: "I want to go there and take such a picture myself."
I hope you do not mind my little ad critique. You don't? Fantastic! I knew you are a great guy!