You're not upgrading, you're sidegrading. If anything, it's actually a downgrade because WebOS on C4 and later models is bloated, slow and full of ads.

And no there is no trade-in for such an old model at HVN.

C4 isn't really that much brighter than C1, not enough for a whole new display change. It's less than a 80 nits difference on a full field 100% white window (very unrealistic scene yes, even in a snowfield). On a 50% window (which is closer to most most scenes in any given movie) the difference is only ~60 nits, which is barely noticeable.

If you want OLED for a room where there's sunlight, your actual upgrade would be a G4 or G5. Honestly speaking I think you're better off with a MiniLED like the Bravia 9 instead.

Just to be clear since someone PM'd me about the C4 after your post; the C4 is very noticeably brighter in specular highlights below the 10% window - about as much as 180 nits brighter. But since you're going to be using the TV in a room with sunlight pouring in, the entire screen still isn't bright enough to combat sun glare either ways.