Was going to make more then one thread on each thing in the right places...but I'll just round them all up in one go.

These are things in other FF games, yes...even FFXI...that I enjoyed greatly or generally made the lore of a real world FF game better.

1. Scrolls
I loved the concept of buying scrolls for spells from many games, not just FF. Going to different towns and areas to buy them or from monster drops and quests.

2. Debuff spells
Where did they go? Choke, Rasp, Frost, Burn, etc. I miss debuffing. It doesn't seem like a very deep game without the option of using such spells regardless if you want to argue they're overly useful or not.
And never forget Tractor!

3. Invis/Sneak
A FFXI spell combo I found very fun and gave an excuse to make the world much more dangerous...forcing players to Invis and Sneak just to get by in many cases. Was also fun just running around aimlessly invisible around town and popping on people. Simple fun to complex necessity.