If I'm reading you correctly (and you're addressing the earlier question on extra scroll copies), you seem to think that copies of scrolls are needed to upgrade. They are not.

You only ever need one copy of a given spell. Upgrades cost crystals, but do not require another scroll copy.

Extra copies of a spell should be sold, or used in combat to cast the spell at level 1, without costing mana.

Nope - I was trying to answer his question about higher skills not scrolls. I might be misinterpreting the question, however, as it was not very clear.

Yep, that's correct.

I tend to sell them.

As long as you have mana points to open your spellbook you can use the extra scrolls to cast spells without using any mana. Also if you have your trade skill up you can sell the scrolls you won't use at any castle for some good money. I sold 75 scrolls for over 100k. Plus if you want to buy a scroll you need to be under the your max scrolls number allowed.