I don't believe for a second that aero will become less significant in 2014. If we consider that the rules from 2012 and 2013 are almost identical, and that McLaren had the fastest car at the end of the season in 2012, I would argue that RedBull has worked on a lot of details rather than dramatic changes since 2012. As little as those details appear when looked at in isolation, put together they are responsible for RedBull dominating the field. Therefore, the sum of small details can indeed make a huge difference and I believe this will be the case in 2014 as well.
I also believe that engine manufacturers have a much bigger impact on aero than it might appear. It is true that a more powerful engine will compensate for higher drag wherefore you could run more downforce, but it's also true that an engine that runs hotter will allow desigers to design smaller sidepods and to pack everything more tightly - therefore reducing drag. It is always a trade-off and it will be interesting to see how things work out next season.
A key metric next season is almost certainly going to be reliability. In order to finish first, you need to finish first. I have a feeling that the fastest car might not necessarily lead the championship mid-season, but the car that is most consistent and found the right balance between speed and reliability. Whether or not Newey will be conservative enough with his approach shall be interesting to see.