I don't think prices today will bot fall to 2005 again. Reason being back then there was an over supply of HDB flats. With HDB flats' prices being lower, there is a wider gap between public and private housing. Thus private property prices were able to fall to such rates.
However, since HDB has now limit the flats that it builds and mostly go for DBSS or other buy-first-build-later schemes, over supply of HDB flats is unlikely to repeat again. So the gap between public and private housing is much more narrow and HDB prices is unlikely to fall much with supply now fixed.
For me, I have just very recently bought a about to TOP private apartment 3bed 1087 sqft in D15 at $650 psf. Everybody tells me it is a very good buy, my banker, the lawyer, my colleagues and even the property agent. I think I have struck gold! hehe.... More so after finding out that the 2nd floor unit was sold for $880k while mine on the 3rd floor was bought at $706k from developer.
There are definitely good buys around. Just keep a look out for those gonna TOP or fire sale units. Mostly developers want to sell them fast as the original buyers either defaulted or didn't secure a bank loan. However, check the smaller listing websites instead of the major ones.