MM and SM are Singapore's special ambassadors and envoys, forging close diplomatic ties with countries effectively. So, how is it they never contribute in their titles?
The contributions they made are PRICELESS.
When you are dealing with cross-cultural ties and relationships, you do not send a "green-horn" or a newly minted minister there. Particularly in the case of Asia, do you think any random minster will be received personally by the Premier of China or Prime Minster of Japan? Even for the Middle East and USA, MM Lee Kuan Yew is always received by the leaders themselves.
In company context, this is the same. If one is truly interested in getting business deals done, one would send the best qualifying person for the job. You don't send a supervisor or young assistant manager because the other party would not treat you seriously. They won't even send their manager or GM to meet you, they will too send their lower-in-rank managers. This is the truth.
If it is that easy, richer countries would not have to suffer from brain-drain and lack of qualified leaders for the posts. If money can buy you security, Venice would not have fall.
Do you think spending an even bigger sum of money on advertising Singapore would fare better than the irreplaceable human touch? It's all about "guan xi" and titles. That's how things roll.
When that "touch" is the heavyweight MM, it shows the other world leaders that Singapore is serious about getting things done.
With MM's charisma and reputation, I'm sure there will be many opportunities where world leaders would still want his advice, but with an official title, it's always a better thing.
Yes, new minsters must take the helm. But that would take time to build up the amount of trust and reputation that MM and SM enjoy.
A thought, he could be earning much more than what he gets if he goes private. I'm sure a few million is nothing to international corporations. CEOs are earning a few times more than what Singapore pay our senior ministers...