Ever since Flyff started, the Vacuum and Earthquake cards were merely used as a joke because popular cards such as Lightning and Volcano are more effective in the long run especially for end-game equipment. I hope I can offer some ideas that can make these cards viable for situational events.

First off we have the Vacuum Card.
Probably the least used if not unused at all as FP can just be replenished with Vital drinks especially on this server where the Vital Drink X can be bought for a good price from the Premium Shop NPC and there are only few skills that require a lot of FP like Templar skills.

What I would suggest is to rework them to give EXP instead. With the same 4/7/10% rates.
Who doesn't need more exp? This gives a small, but good boost on exp for leveling and especially prestige grinding players while not being a total replacement for amps'. This comes with a bit of risk if you are previously using a suit with Lightning cards as you will notice a drop on your DPS resulting in slower kills.(may be different to others)

For the Earthquake Card.
DEF is one of the most important stat you'll need as a Tanker as you need to absorb as much damage so you can heal up before the next attack. Unfortunately this card has been overshadowed by the Volcano card which provides HP instead.

There are a lot of options that can be useful to players ranging from cooldown reduction, extra soul leech or even twice as much DEF but I couldn't narrow it down! I'd love to read other people's opinion for this card if not left untouched.

If ever any rework has to be done on the cards, it would be nice to have a complete wipe for the Vac and Earth cards if possible so it prevents potential hoarding prior to changes to sell for profit.