Not Major differences, but enough to persuade me to sell my Y reg GS to buy a Twin Spark model three years ago.
The Twin Spark is mainly to give a leaner burn engine for emmisions control, but it makes for smoothe running & better fuel economy too.
The headlight is better, because it has a clear lense & a better reflector.
There is a remote positive connector for jump starting (check the battery location

).
Not sure about the Dakar, but the GS came as standard with an aux power socket.
The rear light & the locking tail cubby hole are strengthened (known weak point on originals, see TT catalogue). The rear is already a useable rack when the original ones needed a rack added.
All small changes, but enough to make a difference. Main thing missing from the Dakar is a centre stand.