asdfg2, please don't flame. There is no need to resort to ad hominem attacks. You make a really big assumption when you say that the people defending Singapore's defence posture are all teenagers who do not know anything. You cannot know if these people aren't SAF officers, or their Malaysian counterparts. Respond to the ideas, not the people.
Whether or not war with Malaysia could be won easily depends on your definition of "winning". If winning means defeating the Malaysian Armed Forces in combat, then yes, our victory is virtually assured. We outnumber and outpower them in every way, by margins of two or even four to one (twice the manpower, four times the armor and aircraft, etc). However, this is only the first small part of winning a war.
We then need to hold the land. If the population is hostile (and it probably would be), this would take tremendous amounts of manpower and political will. There is also the threat of guerilla warfare, which the SAF is poorly equipped to fight. Look at how Israel's occupation of Palestine is going.
There will also be the political consequences. Invasion and annexation is forbidden under the UN Charter. We would straightaway become a pariah state under embargo, like poor Iraq. This would destroy our economy, which would completely defeat the entire purpose of any conceivable invasion. We might even face an international armed coalition.
We have no reason to invade Malaysia. Never had, and never will. We have done great without natural resources, and they would do us little good given the current orientation of our economy. We would capture land, but that land would already be inhabited, so it's not that things get that much less crowded. If anything, the less affluent and less educated annexed population would drag us down. This is even before you consider the tremendous human, economic, political and moral cost of an invasion. What possible benefit is there?
However, if Singapore were forced to defend herself, she would almost certainly need to capture some land around her. That is why the SAF has to be so strong -- we must attack in order to defend, and attacking requires much greater strength than defending. What happens after we create the strategic depth around ourselves to defend effectively becomes the question. Do we give it back once the conflict is resolved diplomatically? I believe that we should for the reasons I've touched on.
Happy now, asdfg2?

The people you hear on this forum aren't generally warmongers (except maybe tripwire *joking*). There is a difference between "invasion" and "preemptive attack for defensive purposes", even if both involve Singaporean troops on foreign soil.
However, as our military strength climbs, there will always be the temptation to use it rashly. In fact, a well respected military journal claimed recently that Singapore would have an expeditionary armed force by 2005 (which is probably what spurred the Harimau article). That is ludicrous -- our soldiers have jobs back home, and can't spend their time traipsing on international adventures. That is the worry that I have -- the possibility that a crazed future Singapore government might activate the SAF, not counting the cost beforehand.
Let us pray that never happens.
About having an army without an economy or an economy without an army -- neither is possible. You do not own what you cannot defend. That is not just what I believe -- investors believe it too. If the SAF did not assure investors that Singapore is credible and safe, there would be no investment here, by locals or foreigners. Part of the cost of running a nation is the cost to defend it, in the same way that part of the cost of running a stock market is to ensure its credibility by enforcing rules and eliminating fraud. It is inescapable, two sides of the same coin. Think on this, asdfg2.