No, upgrading no longer makes sense here, the CPU and the mainboard are definitely too old for that. In addition, a new mainboard is very difficult to install in an old Medion anyway (special form factors, only "Medion" connections).
May we know what you need the PC for?
It is an SSD with an M.2 interface. At least as far as I can see. So it's pretty sure that it will be somewhere in the range of 3-5x faster than an SSD that is connected via SATAIII. But I would still ask explicitly. Because there are gigantic differences, especially with M.2. :)
So in terms of price/performance, you will hardly find anything better in this price range, unless you perhaps assemble your PC yourself and cut back on certain components.