I'm just one of those play for a couple of weeks every 6 months types, and I only do solo content (world bosses aside), but if you want players like me to play strikes, a shiny reward isn't going to do it. At best it might get me to do it just until i get the reward, but I'll immediately move on afterwards.
A couple things that would make me more interested in strikes.
1. some sort of automated lfg. I know, I know, apparently guild wars 2 is like Destiny 2, where it's just impossible to have lfg because it's just that hard or something, but that would help a lot.
2. make them easier. Like. a LOT easier. I don't know if that means having different difficulties that are basically comparable to the solo instance except with more players, but that would give someone like me the confidence to try harder group content. If I had the expectation that I had a very good chance of succeeding in 'easy' group content, then I would be more likely to try it. I get that for a lot of vets, this IS EASY group content, but it's not for me and others like me. I don't enjoy failing multiple times in a row, especially in group content. I feel stupid, and it just makes me move on to other things that I do enjoy.
I know, these are probably awful things for more veteran instanced content players, but that is what it would take to get me to consider joining instanced content. I need first to have fun before I consider pushing myself into harder content. If I'm being pushed off the deep end (yes, for me it is) to get a shiny, I'm not going to enjoy it.
Just one very casuals opinion though.