The chances are that the cheap components are, for low end use, like most of ours, perfectly adequate. The chances are also good that should one fail, it will be easily and cheaply replaceable. I've had two cards fail (one US Robotics, one a Pinnacle) since I started with PCs, neither of them cheap, no-namers. The bits that do tend to fail are the ones with moving parts, like drives, and the fans in power units.
I recall that Compaq gained a name that they probably didn't want by using non-standard parts that could only be replaced at high cost, while at the same time the no-name specials made from standard bits just chugged on, and gave exactly the same performance.
My rule of thumb for several years has been to get one contained in the biggest, plainest, box that I can find with the biggest power unit, then fit it with an adequate MB/CPU. If its going to be used for anything higher than looking at photos and writing letters, get a display adaptor, the on-board graphics are usually nearly adequate. Over the last 6 years, I had one MB change when I moved from W98, and a more recent one when one of my drives went a bit wonky, and the SATA ones were cheap enough to "justify" chucking a new MB in. (So my PC is a bit like my grandad's hammer, same hammer, umpteen years old, just three new handles and two new heads...)
The actual machine itself is unlikely to slow down over time, but the programs it runs will tend to gain bulk that will only fit comfortably into a faster running machine with more memory and any new toys bought for it might demand a newer operating system. The corollary is also true - a new OS might need new hardware.
If the Medion is a good spec at a sensible price, I would consider it very carefully. It is difficult to stand in Aldi and look at their spec, then remember what it said while you look elsewhere and try to work out which is the better value, but, having had a play with one of their products, they are good.
Having said that, for video work, there is no such thing as "enough" memory, "enough" speed, or drives that are too big. Being able to dedicate a drive to the video file handling will help, as well, so a board that can handle a few drives is best.
