I don't know about most of you guys, but these girls have a potential if we see some more of them outside of being big bullies. Silver Spoon and Diamond Tiara. What's another word for tiara? Crown. What do crowns symbolize? Leadership. We've seen Diamond Tiara take the role of leader before and she wasn't half bad. And when the CMC stopped reacting to 'blank flank', she knew what to go after (teasing Scootaloo for not being able to fly) and the exact reaction they'd give (Getting Scootaloo sad about her 'disability' and Sweetie Belle and Applebloom getting upset). When leading, you want everyone to agree with you by pointing out faults in a different idea and knowing how everyone will react. Example: Say a pony named Golden Case was running against Diamond Tiara in an election for mayor and he promises to give the Pegasus less hours so they can get better jobs that pay better. Yes, a tempting offer. Who wouldn't want a better job while still controlling the weather so you can afford a few more better things and get more food in bulk instead of going to the market weekly. Diamond Tiara would easily point out that would mean there would be more to do in a shorter amount of time and less jobs for other ponies, and who wants that? More ponies would turn against Golden Case and vote for Diamond Tiara. Maybe she could be in the government when she grows up. Heck, maybe even mayor like in the example!
As for Silver Spoon? Well, she might be a good cook or food critic. Spoons are used to eat with and since she's a bit more wealthier than most ponies, it had to be a bit fancier than a beat-up old spoon. Since I don't have a lot to back up Silver Spoon's cutie mark, this is kinda it. We don't see Silver Spoon being Silver Spoon a lot, she mostly just go along with what Diamond Tiara says and this makes it impossible to see how Silver Spoon acts. It's hard to say for sure what her cutie mark means since both Diamond Tiara and Silver Spoon are never really seen outside of school and "Twilight Time" where we see them in a few select places. Maybe she'll open a five (or more) star restaurant when she's older or a highly respected food critic that ponies turn to when looking for a good restaurant with good food, employees, atmosphere and a reasonable price!
But since it's never explained how they even got their cutie marks, we can't know for sure how they got them. So as for the time being, these are just theories.