I LOVE background ponies. To me, however, the "main" background ponies aren't as interesting as the BACK background ponies. Those who have barely got any attention from anyone at all. Such as Picture Perfect, Action Shot and Care Package... (As seen in order under the spoiler tag.)
They all have official names and appearances, but no one gives a flying fudge about them and who they might be. Now, this is very interesting to me; to see who these ponies could turn out to be. It's not like creating an own OC, but it's to make your own headcanons for already existing ponies. I know that already happens for example Sobra, Discord, Applejack, people assume things about their past that isn't officially announced are true. Many people have their own headcanons for even the main characters, that already gets a lot of attention and story to them. People make up stories to why Sombra became evil, if Discord was a pony back in time, how Applejack's parents died, etc etc. I think it's only natural to develop headcanons for the background ponies as well, that way.
I have several background ponies in the BACKGROUND, that no one have ever noticed very much. I've gotten into them, and made my own image of what these ponies might be capable of and what their personalities are like. They are all so pretty and well planned in their design and name, they've got a cutie mark, but then there's nothing more to them than that. That makes me curious to know more.. And since I'm such a big fan of unknown things, pretty color schemes and cute background ponies... I'm more than willing to take these ponies on to discover what talents they've got, and so on.
I think that the background ponies and those designs that doesn't get as much attention is far more interesting than the ponies everybody talks about and knows about, such as the mane 6, the princesses and the main background ponies; Vinyl, Lyra, etc. These ponies that I've discovered are special, unique and unknown and that really catches my interest.
I personally see it as a chance to use your fantasy and be creative, creating a character personality by only looking at their name and appearances!