After a hearty discussion with my wife, we decided to stay put at our current wonderful hdb flat for another 1.5 to 10 years. The good news? There is currently a straight bus to my wife's workplace and it only take 20 to 45 minutes travel time. In a scenario that we can't move so quickly, our lifestyles should still be quite optimum.

We would aim for a 4 room hdb flat, capped at $400,000 and sell our current flat at $580,000 to $600,000. (Considering the property cycle. Buy high/low, sell high/low respectively). Why not a "free" 3 room flat? (click here). Well, it could be my 3rd property at older age? I would love to provide an EXTRA space for my family while I still can afford. 
(Seriously, why a HDB flat can be so costly? Just a tiny PUBLIC space that we lease for 99 ......