Once a year factory service on the VS? Used to be so---now they have a "reccomended service schedule" just like a car, based on "hours of use". So, unless you're a once a week fisherman, count on multiple servicings a season
But, they are serviceable yourself. If you're that serious a fisherman that you're considering paying $300+ for a spinning reel, learning how to service it yourself makes sense. And, a VS is nowhere near as complex inside as a Sustain.
If you're using a Sustain near salt, it has to be serviced at least annually. Most shops are going to hit you $25 or so to get it done.
When you compare VS to "whatever" weight-wise, make sure you're comparing apples to apples. A VS 150 has comparable weight to a Sustain 4000 and holds at least twice as much line. Both the VS 200 and 250 weigh less than the Sustain 5000 and 6000, and again, have over half again greater line capacity. And the VS 300 weighs about 5 ounces less than the biggest Stella.