I’ve just recently had the first (600 mile) service done on my Suzuki GSX650F (my third motorcycle BTW) and I strongly suspect that it’s “just an overpriced oil change and cable check” as you say; especially as I had accumulated the 600 miles about 10 days after leaving the dealership (I commute).
I would say that the oil and filter change are essential, and the chain lube and adjustment (if necessary) should also be done. You could also make sure all fasteners are tight and lube cables/check free-play too. Other than that, in my opinion, it depends how long it takes you to accumulate the miles. That said, you are the arbiter of your own safety in this regard.
For peace of mind, if you can afford it, get the service done at the dealership. If not, then at very least do what I’ve outlined above.
I would say that the subsequent services (every 3K or 4K or whatever) are essential for safety.
In between times, clean and lubricate your chain every 500 miles, check and adjust the chain tension (if necessary) at the same time and regularly inspect your tires, brake pads and fluid levels.
My recent first service (S.F. Bay Area) cost $229 and that was with their 10% off labor “deal” (normally $110 an hour).