What are your priorities?
As a LH *G I was treated to lounge access in both SIN and MLE
but just the dreaded *G lounge.
It seems you are not interested in visiting the KrisFlyer Gold Lounges in SIN. Why make such a fuzz?
Any way to get at least lounge access and negotiate the baggage benefit with SQ as they are responsible for the downgrade?
The easiest way would be for SQ to reimbourse the additional baggage fee.
It might be worth asking SQ to increase your luggage allowance on the MI flights.