Let's put it this way. Going from the $1499 model with 2.4ghz/8gb/256gb, if you had more money to spend, I'd grab the 2.6ghz upgrade, 512gb upgrade, 2.8ghz i7 upgrade, in that order. Then if you still decide that's not enough, THEN I might consider the 16gb ram upgrade.
If you don't SPECIFICALLY know that you will need the i7 or the 16gb for, it's pointless to get them. As in, if you are even asking yourself oh should I get this to "future proof" my computer, then you shouldn't.
You SHOULD get those upgrades, however, only if you know specifically what programs or specific usage that you are going to use to warrant the i7 or 16gb, and wouldn't even consider the laptop if it didn't have those. Then again, if you knew what you need it for, you wouldn't be asking for advice on a forum.
The 512gb SSD for $200 and the cheaper $100 CPU upgrade to 2.6ghz(1200mhz for gfx) is much more justifiable if you just wanted something "nicer" just for the hell of it.
Just to give you an idea of what 8gb of ram is capable of... I'm playing Guild Wars 2 on screen 1, streaming and recording video lecture on screen 2 so I can play them at 1.75x speed, about 15 tabs open in google chrome, streaming pandora in the background, having adobe and word open to the lecture slides. All that uses about 6gb of ram... on windows 7... OSX mavericks and windows 8 both manage ram so much better than that.
Bottom line - if you have to ask whether to get the 8gb or the 16gb, you won't need the 16gb. If you do actually need it, you know already and wouldn't be on the fence about it in the first place.