Very interesting to read your comments and see your video. You have inspired me to have another go at using effects with my dulcimer.
I have used a Myers pickup and fed this through my Line 6 Pod HD500X (which I imagine is similar to your Boss GT-1).
I am getting some nice sounds with a little delay, chorus and smart harmony. Must have a go with the Pitch Glide effect.
There is certainly plenty of inspiration out there. Apart from your own Sam Edleston, who is very prolific as a member of this group, there are some British members - Duncan Gibbs and Dan Evans. Apart from on this site they can be found using effects on the dulcimer if you search YouTube for English Dulcimer (for Dan Evans) and Duncan Gibbs Dulcimer.
I have not put links here as I think it is against the site rules as they are not my videos.
Dan Evans also has a website, which has an article on amplification and effects which might interest you
Good luck with your experiments. I would be interested to hear how you get on.
PS - I just came across an article which you might also find interesting. I wonder if it would work with the dulcimer?