I hear alot of people talking about waiting a few months for the price to drop. Yeah you could do that. Or you could think about it this way:
You're essentially going to be using this phone for two years. Granted, you could buy another phone off contract but for the sake of argument let's assume it's 2 years. You shouldn't look at the price of the phone as an upfront cost. Consider the cost of the phone over 24 months. Let's not consider your phone plan costs because I'm assuming that it remains the same when you upgrade from the 900 to the 1020.
When you look at it that way, we're talking about a monthly cost of that phone for 24 months being about $12.50/mo. Now ask yourself: Am I willing to pay $13/mo to use this awesome phone?
Now let's make some assumptions. In two months, the price will drop by about $50 (assumption). That drops the cost to $250. 250/24 = $10. You saved $3/mo on a 24 month contract by waiting two months. Is it worth it? To some yes, to others no. That's based on your own threshold.
Again, these are assumptions and this is taking a look at the phone based on the entirety of a 2 year contract.
BUT! There's a way to save money on the phone immediately. When the phone is available for pre-order, call AT&T retention department threatening to cancel. Talk about how other companies have the same quality devices and same quality network and they're offering you deals on them. Talk about how you were thinking about the Galaxy S4 or the HTC one and maybe jumping ship to Verizon or Sprint. Tell them that you have a ridiculous offer with them (maybe make up a number...say bill credit of $30 for 6 months plus a free S4). Ask them that the only way you'd consider staying is if they can offer some sort of bill credit AND knock the price off the Lumia 1020. You like the phone, but you don't "$299 + tax" like it.
They'll put you on hold, talk to the manager, come back and possibly offer you some combo of bill credit and/or (likely or) knock off $50-100 on upgrade price to 1020. Reason is because, and you probably know this, AT&T makes their money by locking customers to a 2 year contract and then shafting them as hard as they can on monthly bills. They couldn't care less what phone you use and how much you buy it for.
$299 is just a way for them achieve whatever margin they can on hardware, and then be able to create attractive promotions in a couple of months.
Conclusion: I personally would be more than happy to pay $299 for this phone but I would certainly try calling ATT retentions to see if I can get a better deal.