You don't need electronic shifting.
But you'll want it!
Have you tried it out yet? If not, you really wouldn't know what you're missing which is great because frankly, it's probably not much unless you really care about how it feels to switch gears. I've also heard that 105 and Dura-Ace is basically indistinguishable unless you go electronic so you've pretty much got as good as it'll get in terms of switching.
Disc brakes are also not necessary but you may want to consider them for your next bike or if you're going to drop money on expensive wheels.
If you want to adjust your reach, maybe just swap out the stem? As for a new bike, that doesn't need to get justified. Just get it if you can afford it and want it.
surak makes a good point though: if you do go the new route, I'd wait a bit for the new models or for the current ones to go on sale.