That's not necessarily the case because the bulk of the money that I made as a Sinkie was transferred to Australia when I left Singapore so you can't assume that foreigners suck money out and that sinkies bring money in.
As long as transaction take place, there is money to be made. Foreigners need to spend money while they're in Singapore. They can't live on love and fresh air.
In a globalised world, there will always be inflows and outflows of money. This has been occuring for a long time, even before the 20th century. The Opium War had its roots in the outflow of silver (which was used as a medium of exchange i.e. money back then) from Britain to China. The Brits had to pay cold hard cash (silver) for tea, silk, porcelain, etc and the Chinese did not covert anything that the Brits offered. Opium grown in India was the Brits' saviour and the Chinese's nemesis.
Back to the topic. I assume that you left Sinkieland because you were unhappy about the political situation, the typical Sinkie's attitude, blah, blah, blah. In other words, you and your money might have remained in the Little Red Dot if the situation was different. Your somewhat "loyal" money fled. The Sinkie Government instead of reforming things to keep and attract "loyal" money, decides to take the easy way and attract hot and footloose money.
Yes, as long as there is a transaction, money flows, but there are many types of transactions. Upon advice and guidance from an eminent Dutch economist named Winsemius, first generation MIW attracted the right type of transactions - foreign money that came in and sunk roots by building factories, training local workforce, etc. It is not that easy to balik kampung when you have already sunk in millions into building a factory. On the other hand, it is very easy to withdraw money from an account kept at a private bank. You can do it the moment you no longer feel at ease leaving your money in Sinkieland. Even if that moment occured while you are partying with a group of pretty young things in a little rock called Monaco. Just pick up your mobile and call the private banker to quickly transfer everything from your Sinkie UBS a/c to your Swiss UBS a/c.
Cheap foreign labour (including those at the PMET level) that is physically in Sinkieland spends money too. However, they are not likely to be spending big money. The reason why they are imported in the first place is because they are cheaper than locals. The collateral damage is big - they will be taking job or advancement opportunities away from the native population who can be presumed to be more loyal and rooted had the Government not pissed them off with crap policies. The quality PMETs amongst the locals, like you and me, will see the writing on the wall and flee, and like you and me, will take the bulk of their money to their new place. So, a virtuous cycle is replaced with a vicious cycle. All due to Sinkie government's short term obsession with GDP growth to which ministerial salary is pecked. Recycling votes (fussy Sinkie PMET votes replaced with new citizens' temporarily "grateful" votes) is another prime motive behind all these.
What is good for an individual at a micro level is not necessarily good for an entire nation or economy at a macro level. Economist Milton Keynes realised this decades ago. Ministers who are paid out-of-this-world salaries should know this too or they are not worth the money.