Seal scroll fragment actually has less value than mangatama. You trade 5k points for 12.5cp worth, while 2x random mangatama is 2*(12+12+15+15+15)/5=27.6cp for 5k points. Medium thread has the best value of 38cp/5k points. Summon scroll fragment has a value of 12,6cp/5k points. (all shop prices)

As for items you can sell- sell basic/medium/adv cloths once you get past their level, they give a pretty nice ammount of gold. As for any items, that can be sold for 1-100g, imo its not worth it. Maybe they will be able to be used in a better way in the future.