As a 5d3 owner i remember the kick when i first tried the 5d3 owning a 5d2 this time, and yes it was iimmediately visible that it s much better and almost every way, except sensor prerformace which was the same.
i tried a 5dIV and the difference is much less obvious, at least in 5 minutes in shop.
For me, the biggest advantage would be the almost ISO invariant sensor, which would allow to underexpose at low iso, brighten in post ans so avoid blowing highlights for night shots. The other upgrades may be there for sure, but they wont save me if i am doing things wrong, or with other words, it's most times users fault if one can not take a good shot with a 5d3.
So i would really like a 5d4, BUT so far, i was not ready to spend 2000$+ for the upgrade, better get a speciality lens for this, or other equipment like a really good tripod, or take some lessons in photoshop.
This question may be a matter of luxury, if you have everything else, have no training needs, have enough money for travelling whenever you have the timee, and still have the money, i am sure you will really like a 5d4, as i would like it