So, if this is the 2020 4.0:
https://www.specialized.com/us/en/turbo-vado-4-0/p/170303?color=273963-170303
and this is the 2020 3.0:
https://www.specialized.com/us/en/turbo-vado-3-0/p/170305?color=274059-170305
The motor is the same, just tuned for efficiency on the 3.0 (1.2E). The battery is a 460WH on the 3 and a 500WH on the 4.
From a power perspective, you may get a slightly longer riding time on the 4. Peak power on the motors, though, will be the same. While I've ridden neither, I've had both motors - the regular 1.2 on my first Como 2.0 and I have the 1.2E on my Como 3.0. As far as capabilities, they are the same. It's not apples and oranges, though, because my 3.0 has a 48 tooth front chain sprocket, whereas my 2.0 had a 40 tooth, so the feel is different. As far as top speed, I hit the max speed - 19.5 mph - well before I get to the ninth gear in the back.
Both the 3.0 and 4.0 seem to have the same bells and whistles. So, if the derailleur, brakes, cluster, and anything else is better on the 4.0, I THINK that's what you'd be paying the extra $1K for. If it were me, I'd stay with the 3.0 even up.