Now that we have a method of installing game dumps on to our consoles (thanks to HENKaku), we still have the issue of expensive memory cards. These PSVita memory cards are incredibly expensive when compared to their MicroSD counterparts.
Luckily someone is working on a memory card adapter. RichDevX! He made a tool to interface with the card’s host controller, but now he has started developing the actual adapter. Here is his last tweet on the subject. Hopefully we will see some kind of screenshot of a working prototype this week. Be sure to follow him, as when he launches these types of things they tend to sell out fast!
Personally I would buy a 128GB micro SD card if the adapter allows it. Some games can be about 1.5gb in size, others can be 45mb. It just depends how many games you want to install.
If you want to learn more about HENKaku, check out the project page here henkaku.xyz. Keep in mind that HENKaku just opened the doors for homebrew to be installed on the PSVita, they are not the ones who made the homebrew that lets you dump games and/or install game dumps. That would be the Vitamin homebrew project.
UPDATE: With VitaShell v1.61 you can now use a USB thumbstick as a memorycard on your PSTV!