I think S&V is pretty common in 3.5 doubles particularly among the more successful teams. I play 4.0 in our all doubles local league and have played up at 4.0 doubles in USTA and I'd say the same thing about those players--the better teams get to the net at the first opportunity whether they are serving or receiving. In singles I don't see much S&V but the guys who do it tend to be at the upper end of 3.5. The only two S&Vers I played last season got bumped to 4.0.
When should you serve and volley in doubles? Only when you want to win.