This is a hard one, because the power to displacement ratio is pretty good, considering the design isr 30 years old.
Things like pod filters make no difference on just about any car, so forget that. The exhaust does sound nice when a 2" is fitted, but I can't say the gains are noticeable on the CB23.
I do advocate a modification to the vacuum hoses, that allows a few degrees more advance and better pickup. You swap the hoses like so
and advance the timing about 12mm on the flywheel dimple. It still allows starting because the dizzy isn't allowed to adavnce until the throttle snaps open, unlike the stock piping setup.
Note where you existing hoses are in case you want to swap back. When you make the mod, listen for pinking up hills and retrad the timing a tad until it stops.
Although there is minimal power gain, the Bosch Super 4 plugs are great for eliminating misfires and regular maintenance.
Make sure you keep the points gap at factory. If you can source an electronic dizzy and coil from the 1990's era G200 series you will notice increased torque and nvere have to worry about gapping points again.
Empty the gearbox oil and replace with Redline
Check your engine mounts aren't splitting. Any undue flex will load the CV joints and you will lose power to the wheels.
The G11 has a rubber bushing on the gear selector control rod that wears away causing the gear stick to wobble as you drive. Replace this with an OEM bushing or make one yourself from some rubber hose.
These are peripheral mods. If you intend getting stuck into the engine internals, there is head work you can do, plus a new set of rings and bigend bearings will freshen up the power.
You can also try to source a CB60/61 engine and enjoy the spirit of a turbocharged engine.