The higher level the spell is, the better it is to junction (like firaga is better than fire) and the more spells you have, the more it will boost your stats (75 fires will make your stats higher than 20 fires). You should teach Quezacotl the card ability and card mod ability and refine your cards into useful items. Life spells like Curaga and Regen (I'm not sure if you have that at this point) are great for your HP. So you should always try to have like 100 of the spells you're junctioned to, or a really good number so it doesn't bring your stats down, that's very important.