Im in the same boat, got 2x1070, 1x1050ti running and would really like to expand...

But in my opinion its very risky at the moment as GPU prices are still super high but coins are low and falling. There are too many people jumping the hypetrain without doing the math so the GPU prices will stay up and difficulty keeps rising. Im at 0,15$/kWh so i think i will not upgrade my system as ROI for 1070 here is above 1 year...ffs i believe Ethereum PoS will be sooner than all the ppl who buy 1070s now ROI...and thats going to change the mining world.

Running after the hype is never good. Good moments to buy hardware are in my opinion when the coin value is high or when there is a new coin that has something real to offer and is worth mining early and hodl, but all I see is ICO scam and worthless copypaste coins that wouldnt earn a dime without hype.

So i will wait another 1 or 2 months and reevaluate the situation