A: Yes. Copy the SAVEDATA folder from your PSP (connected via USB) to the PPSSPP/memstick/PSP/ folder on your PC.
Downloading a completed save data file typically unlocks the following "end-game" content: gta vice city stories ppsspp save data
The Ultimate Guide to GTA: Vice City Stories PPSSPP Save Data (100% Completion & Unlockables) A: Yes