It depends on what you want out of the cards.

As long as you have a computer or PS3, moving all of your content to a new memory card is fairly painless. Here is how you will do it:
With old card in, plug the Vita into a PS3 or PC.
Open content manager and backup your data.
Completely turn off the Vita (hold power button and select "power off"
Swap the old card for the new card and restart the Vita
Plug back into the PS3 or PC
Run content manager to restore your backed up data.

If you plan on actively using both cards, it's pretty annoying. If you ever want to switch cards, you have to completely shut down the device and swap the cards. When it comes back up, the icons will likely be all messed up and out of order. When you have 7 pages of icons.. this is unbearable.