Over time dust can build up in players and make it hard to read discs. While cleaning discs are sold, they're not really recommended. The brush used can actually damage the laser lens in the worst case, and in the best case it only moves the dust around inside the player, which can lead to other issues later.
The proper way of cleaning a DVD player is to open it up and use a can of compressed air. Only do this if your player is out of warranty as this technically will void it. When opening the player be careful as there may be ribbon cables and other wires that can be damaged if you move too quickly or roughly. "Minimal force" is the key word here. Use the can of air to blow the dust out of the case. Make sure you don't tilt the can too much or you'll get liquid coming out instead, which holds a temperature of -40 degrees. While not harmful in and of itself it's a good idea to let the player sit for a half hour or so to avoid any damage.
No Blu-ray, no buy. No lossless audio, no buy.