You can clone it from System Settings, but it would still be system unique. No real way around that I'm afraid, you can dump the decrypted data from the HDD using a PC tool but in unpacked format which you can't do a whole lot with directly, besides run it in Loadiine. Although the data can be packed with nuspacker into installable format again, you need to get the ticket to do so (not that hard), and getting tickets for and packing every game quickly becomes a time consuming task. Downloading games is still easy with Wii U USB Helper so to me it doesn't seem worth the hassle. Just back up the save data and keep it safe.
You got £210 for it? That's a lot for a used Wii U. Hell, it's a lot for a new one.