I'd buy used, but yes I'd sell an older Rolex to fund a new one. Nearly two years ago I sold a Speedmaster for £2150 on eBay that was 8/9 years old. At the time newer big box version could have been bought for similar money, certainly less to change than the cost of a service.
And now I've a 14060m from 2003, again I'd rather sell that on eBay and find something newer like the 114060 that sold here recently for £4800, or the 14060m that had just returned from a service. Either watch would cost me a lot less than an £800 service.