Tough to say. On the handheld front, Nintendo did this with DSi and New 3DS. I think it helped in those cases. The DSi in particular was a success because it added a camera and a digital games (DSiWare) store. But I think those platforms would've continued to sell regardless, so a mid-gen specs boost wasn't needed.
The PS4 Pro is basically the best 1080p console on the market. Even if you have a 4K TV, the resolution is dynamic in a lot of games. Sony dropped the ball not including a 4K Blu-ray drive. If the Xbox One S can have a 4K Blu-ray drive and be very affordable, so can PlayStation. Xbox One X delivers a much better (though not uncompromised) 4K experience. The Xbox One X did not seem to help Xbox One much besides adding 5-7 million more units sold, and the bragging rights of the most powerful console on the market.
I suppose the answer to whether or not mid-gen upgrades would be helpful for the Series X and PS5 are very much up for debate. We'll have to see what developers can squeeze out of the consoles during their lifetimes. Let's just say a game like GTA V would've been pretty unthinkable on the Xbox 360 and PS3 at launch, yet they made them work in 2013.
Circling back to Nintendo, there are debates of whether or not Switch will get a "New" or "Pro" version. If Switch 2 doesn't come out until 2024, I'm very sure they will. But if it's out in 2023, that makes it less likely. The Switch is selling very well, and developers have squeezed some impressive games out despite the spec limitations. I have a feeling a mid-gen Switch update would be more akin to a PS4 to PS4 Pro leap, not an Xbox One to Xbox One X leap.
Lifetime Sales Predictions
Switch: 144 million (was 73, then 96, then 113 million, then 125 million)
PS5: 105 million Xbox Series S/X: 60 million
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima