We are buying 70% of ARV - Repairs since the market is softening up.

Yes, the appreciation isn't going to be there like it will in Cali, but seriously, your bubble is about ready to go out there, and your cashflow will continue here and won't be felt as strong if a softening does happen. 

Also, I do "soften" the news with a businesslike cover letter reminding them of increased costs we are facing...insurance, material and shipping costs, labor costs, yada yada..."

I'm seeing that successful str's and desirable STR friendly properties experience appreciation, amidst the softening market, whereas HOA's governing str restricted properties have taken a huge hit on value.

However, I see both housing and rental market in Las Vegas has softened a lot.

So if that's the case, someone very well may pay the higher price for your asset but the market is softening so I would be wary.

If you are comparing one 4-plex to two duplexes, the tax effects are likely going to net out between the two, and therefore only make the calculation harder to end up at the same point.Additionally, let's assume the market softens so you have little to no inflation, you used your tax benefits, and the property is still cash flow negative.  

Furnace, water system for pressure & softener, sump pump/s, dehumidifiers, dryer hook-up….

I haven't heard any professional investor say that the market won't continue to climb except soften just a little.

BRRRRs are actually a bit easier now than a few months ago (although you should be more conservative on your price) given that the market has softened (easier to find deals) but prices have only gone down a little.