pre-order ASAP of course, why wait!?
There are several reasons.
Waiting for a price drop if the price is too much for you.
Waiting for one or more games that appeal to you so you'll have a good reason to get it.
Waiting for reports of the issues a new hardware is bound to have, if they are big you might want to wait.
Waiting for the full reveal of both it and the new XBOX if you are undecided which might be a better choice for you.
And so on.
Personally if I could get it for a good price I would get it asap because I know the PlayStation will be the best choice for me before it even releases, because it has always been.
But here in Brazil for example what will cost people in USA $500 at launch (I guarantee that's the price) will cost around $1200, and I really don't plan on supporting that kind of ridiculous pricing or even spending that much money by itself, so I'll have to wait a good time until production of the system start to be done here and they slash the price to something like $800, then Sony slash the system price to $400 and some place makes a good deal for $600 so I can feel not abused enough and go get it.
So it's sadly not that simple as go and pre order it asap for a lot of places out there, but sure, if I could buy it for $500 at launch I would go for it without a second thought xD
wait 2/3 years to save 50 to 100$? lol no
there's always games that appeal to me, especially entering a new gen of gaming, especially now that we're looking at near 0 load times, etc
always bought my consoles day one and no issues so far, if anything on the PS3 gen, having the original hardware meant having access to full backwards compatibility while later iterations of the console lost it. on the vita meant having an OLED screen vs having an LCD on the latest iteration
not undecided in the least, know exactly what to expect from both 1st parties
and so on...
sounds like you should take a nice holiday abroad and in the meantime bring the hardware with you, it's ridiculous the taxation on game consoles there, but that's more of a country specific problem, not a real reason not to pre-order