What I did is add 8 extra GB or RAM (I can add another 16 GB and max out at 32 GB) and replace the DVD with a 1 TB SSD. I did the latter recently and I still have the original 750 GB HDD inside. I'll swap them and eventually decide if ejecting the HDD (which is powered off most of the time now) and taking in back the DVD. Not that I used it much, but the model with a DVD burner and the upgrades I did was much cheaper than a custom model with them included.
I don't see me replacing this 2 years old machine anytime soon. It's got enough CPU (i7-4700MQ 2.40GHz), RAM and disk for the time being. Eventually it will run out of service. It's 3 years next business day for less than 100 Euro, I think I can renew for another 2 years then we'll see. It's good enough and my Galaxy Tab S (first generation too) is still fast enough to do everything I don't need a real keyboard for. It's 300 grams and even if it lives mostly at home (8.4" are large) it's a laptop replacement for browsing and viewing videos.
Hardware has got good enough since a long time, the replacement cycles are becoming long.