Whats the general consensus on building a new Vega rig @ todays rates? (Card price vs earnings)
Yes no wait never

Never say never, but currently IMO price/hashrate ratio isn't in favour of vega. RX 470/480/570/580 gives better results.
From pm discussions 4 vega 56's can be had for about 1700-1800 usd put in with a ryzen 1700 and a proper mobo.
Build is about 2200. it will do 8000-8500 for cryptonight/monero under 700 watts. so roi is under a year.
how good is that? I am not sure. What I don't like is if xmr tanks the card does not have a lot of value.