That said, I know they aren’t economical, and they aren’t going to cause significant improvement but a big consideration is - are they as durable?
As far as 'improvement' goes, a lot more depends on things like the rim profile and spoke count than just what the rims are made of.
If we ignore super-light climbing wheels and 60mm deep-dish aero hoops, you're probably not going to see a huge amount of difference if it's say, a typical 20/24 spoke 30mm road wheel. The carbon might have more vibration damping with 23mm, 120psi tires, but your could get the same ride quality with Al rims and 28's for a couple of bills less.
You pays your money, you takes your choice.
