I noticed repaired ships sell better (more units) but does it also yield better scraps? E.g.: better modules, higher chances of storage augmentation units...
Yes, repairing some damaged parts gives you more credits when scrapping the ship:
The trade-in or scrapping value will be reduced by the ratio of Damaged Components to total slots. The normal trade-in value is 70% of that.
According to No Man's Sky wikia:
The value in units of the ship as scrap will be shown before you confirm the option. The value will be added to your inventory in the form of items and upgrade modules. The quality of modules received and their value depends in part on the value and class of the ship. Because the value is given in items, you may get more or less than the amount listed depending on the economy where you sell the items.
Storage Agumentation Units are worth 95.000 credits, so you have a small chance that an equivalent set of scraps will be a Storage Unit, the better is the class of the ship, the greater are the chances for the rarer items.
So, yes, it should help. But it's probably worth it only for A-S class ships, since repairing a C-B class ship will raise its value only for a small amount.
I'm not playing right now but some patches ago (january/february 2021) it was better not to repair them. You want to repair only the flying systems just to bring them to a station.
If they haven't change the behaviour it's more convenient this way
The tier of modules, etc. should be linked to the ship tier. If you scrap a tier S ship, it's more probable to find high tier rewards, so if you want better modules you have to scrap high tier ships