Totally worth the upgrade for me. It's a sexy, sleek design that is so much more portable than before. The battery life is excellent. The display and new aspect ratio is much better IMO. Also, even though many bloggers lament the type cover/trackpad experience, I find it a huge upgrade and more than adequate. I can actually use it as a laptop in bed or on my lap which I definitely could not before.
I got a Surface Pro (64GB) on launch weekend, I got rid of it because of the terrible battery life and small SSD. I got a Surface Pro 2 in December, and I was much happier with the improved battery life and SSD "real estate". This last February I got a Dell Venue 8 Pro (64GB) and found that I started using the Surface less due to the similarity on size, and still used my desktop quite a bit because the Surface Pro 2 screen size was a little small. The Surface Pro 3 seems to be ideal, spreadsheets, and all Office apps, are much better with the bigger screen. As far as keyboards. I had the first generation Touch for the Surface Pro, the Type Cover 2 with the Surface Pro 2 (loved the backlighting), and I bought the new Type cover with the Pro 3. I find the touchpad on the version 3 to be a vast improvement over the Touch 2, with actual clicky buttons. At this point, I think that the Pro 3 and Venue 8 Pro are a great setup for mobile computing.
I have a SP2 , got a SP3 and returned it and now have a Thinkpad Yoga....
I LOVED the screen res and weight of the SP3 - with that being said, the Surface can never be a laptop replacement for me due to the kickstand/type cover design. If Microsoft ever makes it clamshell style ala Asus t300 CHI I would love it.
I didn't like the N-trig compared to the Wacom - Maybe it will get better over time but I didn't like how it felt for what I do
Completely subjective based on need. In my case, great decision as the larger screen makes the thing actually USABLE as a stand alone notebook. Heck, the stand alone makes the upgrade worth it for me. Coming from the SP2, I don't want to go back.
However, if you're mostly docking it to replace a desktop, Those reasons become completely meaningless.