PI3 vs PI4 - do I upgrade?

I have an old Raspberry PI3 (with SSD) that runs DietPI, Pi-Hole and Wireguard. It seems to work fine and never been a problem.

Is there any point in upgrading it to a PI4? PI3 seems to run all the latest versions, but will I see a speed boost with an upgrade? Load always seems to be zero.

I know I’ve swapped out old routers and been shocked at the speed boost. Is a PI4 any faster at doing DNS lookups compared to a PI3?

There should be no need to upgrade. I guess your system is idling most of the time.