As an ex-Engineer I have to agree with both opinions.
I have found disgusting Flight Decks and some things I would probably not want to discuss on a public forum.
Some Engineers are spectacularly clean in their approach to work, usually the ones that sort the FMC out and have escalated themselves to that position. The ones that like to appear on TV with a certain airline - shock horror stuff !!
The type who have long moved on from one end of a screwdriver to the other.
Before you jump, I have done both positions.
There are, of course, other types who have to get down in the dirt and do a - what I consider to be - true Engineering job. Those with the tools do get dirty.
Dirt and misplaced documentation is a burden of any Engineer and also Flight Deck crew.
I think this matter is well raised.
In my previous work - I had to go down into the Avionics bay, I, as a result got dirty, but it didn't stop me cleaning up the switches on the flight deck after I had had my hands on them.
I had a respect for the simple fact that the Flight Crew were going to be there for some time, eating, holding cups of coffee etc etc.
No decent reason why at the end of the day you cannot raise this with your Operations staff as it could be a basic H&S matter if it concerns you so much.
But just as common deceny goes by the way so does common deceny in Engineering staff.
However, look at the bigger picture as an Engineer I say.
You are there to support an airline, Flight Deck and Cabin Crew. They are all equally important to your livelihood at the end of the day.
Basic cleanliness from what you do as an aircraft Engineer is a compliment to the Crew. It doesn't take much effort and is generally appreciated.
Apologies if I have ranted on - a point needed to be made.