How about you do a fresh install and see how you like it? Copy some basic stuff, use it for a few hours? If you see no benefit, just clonezilla, or whatever the cool kids do these days, your current system onto the new drive and be done with it.

I don't expect anything exciting that's actually visible to the user (do you?). What could be different between the two methods is more on the technical side IMHO. I would name 'em if I knew 'em :D , but more like having an old startup system (whatever might be better here), a read-only /usr/ directory, such things.

I've struggled with the same question on my Debian stable home server (same install since 2010), when I replaced the hard drive about a year ago.

Philosophical: I think the problem with most rolling type distros like debian and others is old confs and packages. Apt won't automatically overwrite or update confs you've edited, so it's very easy for them to become stale and eventually cause problems when old stuff gets deprecated.

I would assume there are also potential problems with technology changes. I know some time ago, debian switched out MySQL for mariadb. Apt did the switch for me and removed MySQL with no issues, but I do wonder how projects that might not be drop-in would work, like Wayland instead of x11.

I would say there are two things to consider if you are thinking of copying vs reinstallation:

1) How old is the original install? Are you getting to the point where new stuff isn't working because the configuration is too old (assuming packages are up to date)?
2) How custom is your install? Do you have a bunch of modified confs in /etc or tons of stuff in www-data or opt, etc etc? How easy is it to back those up?

Technical: if you want to copy the installed system to the new SSD, it's actually pretty easy. dd does it without a hitch. I took both drives and plugged them into my desktop and dd'd one to the other. Then I used gparted to expand the partitions on the new drive (and mark it bootable). If you don't have a spare computer to plug them into, you can do it in a "live" environment off a USB stick and do the same thing. I think Clonezilla does basically the same thing but with a nice interface.

Cloning: You can clone the stuff from the old drive to the new drive by booting from a live USB environment and dd $OLD_DISK to $NEW_DISK. mount $NEW_DISK and edit /etc/fstab to mount your partition(s) by block device name instead of UUID(both disks will have the same UUID and will cause confusion at boot, possibly hanging the system or alternating which device it boots from)ex: /dev/nvme0n1p1 /

save your fstab changes and reboot your system. disadvantages of this are that if you are using a full UEFI boot, you may have to go thru some extra fiddling to have a correct UEFI boot entry. consult da googles for more info on managing uefi boot entries with linux.

Fresh Install: probably the best way to go. Install the OS and after installation don't reboot yet. mount $OLD_DISK and copy everything from $HOME to (i'm using Ubuntu references here since that's what i'm familiar with) /target/home/$USER

THEN:

mount -o bind /dev /target/dev
mount -o bind /proc /target/proc
mount -o bind /sys /target/sys
cp /etc/resolv.conf /target/etc
sudo chroot /target

once you've chroot'ed change the ownership of everything under the $USER_HOME directory to the new system's user.

as well, while in the chroot you can do updates and install any packages you want. Also a good idea to install Nvidia drivers if you have an Nvidia GPU and use the proprietary drivers.

once that's done you can reboot into your new OS install.

Only some months later, I decided to go the reinstall way.

KDE's database service akonadi made problems, but then, it also did the last-but-one upgrade. :-/

The new system feels fresh, but every now and then, I have to copy over something from the old system or install something that's missing (I didn't want to automatically install all packages I had on the old system either).