There are a few big things with the European dishwashers (like the bosch, miele etc):
1, they need to be installed properly as per the instructions they came with (not seemingly an issue to the OP.
2, The filters need to be cleaned and then re-installed properly on a regular basis. The manufacturers usually recommend daily to weekly. Do what you think is sufficient as long as it gets done.
3, They use such a small amount of water compared to their American counterparts, that they also require a much smaller dosage of detergent. It will all depend on the brand and type of detergent, the type of water you have.
When i was servicing and dealing with Bosch tech support, they recommend as do I, that a powdered detergent be used in all cases. Secondly rinse-aid must be used and the amount dispensed adjusted based on water hardness (more for harder water, less for soft) for the dishes to dry properly. The amount of detergent used is also dependent on water hardness, and the same rules apply as for rinse-aid. Soft water may require as little as 1.5 tsp of detergent. Also there is no pre-wash detergent cup. So detergent for the pre-wash is added directly to the machine. Again it may require as little as 1.5 tsp. Hard water may require a full detergent cup (which if i remember correctly is about 2 tbls)
And lastly do not under normal use pre-rinse your dishes in your sink. This will effectively double the amount of detergent you add to the machine. IF there is no soil on the dishes then there is not soil to activate the detergent and it may not rinse out entirely during the rinse. Simply scrape the chunks off and go. Sure things like egg and oatmeal may need to be rinsed but what are you gona do.
Old detergent is also a cause of poor performance and or detergent build up. If your detergent is caked or fails to dissolve properly then it may be too old. Moisture can get to it and after a time in the cardboard box it comes in.
Cheap detergent isn't necessarily going to hurt the machine, but will often require to get the same results thus negating the cheap factor. Although some cheap detergents just don't do a good job and require so much that over-sudsing can occur and the European machines are quite sensitive to this because of the way they sense water levels.
If this is the way you already use your machine then, baring any hard-water or rust stains, there should be no real reason to clean the machine out or change detergents.
If you need to clean it or remove an over sudsing condition vinegar will work great. For harder stains like hard water a commercial dishwasher cleaner , like Glisten or Cascade or even Tang will work in most cases just fine.
Hope all this makes sense