Hello everybody! After being away for several years I started playing again. I now wonder, what's worth getting in the Quest Shop and the Blue Building Shop? Certainly it makes no sense to restock there, as everybody can get the goods sold there themselves. Any advice? What do you get yourself there? TIA

I buy all the foods for my gourmand, books for my battle pet and job promotion seekers, and most of the wearables for me.
If you're trying to sell for profit, a lot of people will buy points on the Advertising forums, you just tell them how many points you have, your rate, and they'll tell you which items to buy. If you don't want to do this, seasonal items in the quest shops are only available in their respective season, so probably sell for more sp when they are out of season.
I got me all the plushies and beanbags that are missing in my collection for a start. Now saving on more points for the stickers and some wearables. Is there a ratio where you would say I should buy an item for sP instead of Blue Points?

We can only get 100 BBP per day. It is easiest, we can get 3MsP per day from quests. Compare the cost to yourself in terms of how long you want to wait to get the item, how much effort "doing the quests" seems to you, and how willing you are to give up each currency to get what you want.
That is your conversion rate.