No one can predict the future resale value of anything (and not just computers). You are predicting that the 2016 computer will decline 14% in value after a year, which I personally think is rather optimistic.
Normally how these things work, the resale value decline isn't linear. It'll drift downward for a while and then drop substantially more when the new devices and (and pricing) announced. Then you will have to wait for the new device to ship during which time the resale value of the old device will continue to drop until you get your new computer and finally put the old one of the market.
If you want the maximum resale value, you'd be better off selling the 2016 unit a month or two before the 2017 model is announced. Of course, that will leave you empty-handed for some time, possibly 2-3 months. Another problem is that you aren't guaranteed to know when new product announcements will be. Sometimes Apple releases slightly upgraded models without a media event.
Computers aren't investments, they are expenses.
I try to figure if any given computer/device will better fulfill my personal needs than my current equipment. You don't bother to mention what you do with your computer (or what it even is) so it's impossible to say whether or not the 2016 MBP is going to be any better than whatever you have for whatever it is you want to do with it.
I tend to use computers until their useful life is pretty much over. I have a Mac mini 2010 that I would like to replace someday soon; if the next version of macOS obsoletes this computer, I will buy something then. If my Mac mini 2010 is again spared OS obsolescence this fall, I could keep it around for another year. I am fully aware that it could conceivably fail without notice at any moment and the likelihood of it doing so will only increase as time passes.
Personally, I would not proceed with a discounted purchase assuming that I will recoup all my money a year from today, but again, that is not the way I look at computer purchasing.
I would assume at least a 25% value decline after the new 2017 models are shipping. For this case, that would $2625 from an original list price of $3500. Between your out-of-pocket of $3000 and (predicted) recouped $2625, that's $375 in ownership cost. Is the new 2016 computer worth $31.25 per month for the additional functionality it brings versus your current equipment (for which presumably all costs are sunk)? Only you can answer that.
