I've located a number of properties (I'm new w/ no offers) that are in lower income neighborhoods...a number of which are F&C or very little is owed.  

You can actually beat the 2% rule if you don't mind dealing with a lower income area.  

This would lower the required down payment into the range of 3 - 10%.

You also do not have to sell to realize that value...you can refinance, pull our your invested capital (and then some on this example), let the property continue to cash flow and use the refinance proceeds for the next deal.I was not necessarily recommending this strategy...just adding onto the BRRRR strategy from your initial post and describing the next level of leverage beyond that strategy since that was your question.

If I was to purchase a multifamily investment, for example a 6-unit property, and turned two of the units into vacation or short term corporate rentals that increased NOI when compared to traditional rental income with lower NOI, how would lenders look into this in terms of a value add to the property?  

But, that's me.It depends on the level of risk you're willing and able to take.

Do you feel this depends on the experience level of the investors?

The market is better in the lower rent ranges as the pool of potential renters is larger there. 

My level of quality is high, I stand behind my work, I've been in business over 8 years, its easy to get ahold of me, I'm not going anywhere...That being said, if someone in my area needs a referral of a subcontractor or electrician, plumber, hvac guy...I'd be happy to help if I can.  

I invest in lower B class properties in a strong market (Nashville) where I can cash flow (NOI even after all set-asides for PM, major repairs, etc) about $300 a month for every $170K home I purchase.