In Audacity you can also use Macros so you don't have to import every file and risk audacity devouring your computers performance.
Tools > Macros
In the [Manage Macros] window select [New]
Name the Macro, I'll call it 'wavcon' for this
At the bottom of the window with 'wavcon' selected find [Apply Macro to: Project | Files...] and click [Files...]
Navigate to the folder with the mp3 samples, select all of them, and hit open. Audacity should pop up another small window importing all of them, but won't import them into the actual project.
Wait for it to finish, and once it's done, go over to the right-hand side of the [Manage Macros] window and select [Insert]
Navigate through the [Select Command] window to find [Export as WAV], select it and hit OK.
Hit OK again in the [Manage Macros] window.
Go into your voicebank folder and now there should be a new folder called [macro-output] with all of the exported wavs in it.