Your post makes very interesting reading and I congratulate you on how you manage to maintain your A class yourself. HOWEVER implicit in your post details are a willingness to don a boiler suit and get "down and dirty" with your A class plus an ability to strip and repair a complex vehicle electrical component. I would put it to you these are not necessarily abilities possessed by many A CLASS owners and many would rely on taking their car to their local garage or dare I mention it their local MB dealer.
Now if they are lucky they will have a resourceful and knowledgeable mechanic who will be able to do as you suggest--- at a price
--- but they may well have the experience of--- the fault 25= replace modules X through Y approach so prevalent now.
Indeed at present labour rates plus VAT module replacement [ with a warranty] may be the cheaper option to strip and repair? I think the warnings about the high cost of running an old A class are based more on the more common scenario I have outlined rather than your very resourceful and knowledgeable approach.