Will they be appraised based on income producing or comps?

So at some point they must produce it.

They are fairly easy for them to produce for you.

They typically don’t appreciate it as fast, but as an investor, you should judge the investment being sound by the numbers they produce and consider the appreciation it can produce as a bonus. 

Agree totally with @Matt K....this is the first really good advice I've seen on this site in a long time...Foremost, markets exist in many forms and no two are the same (even in the same neighborhood)...if you're buying duplexes then looking at Marcus & Millichap reports is a waste of time...and CAP is simply an estimate of what investors are willing to settle for...would knowing that your target area is only producing a 4 CAP alter your marketing to sellers as you work on your next acquisition of a deep discount deal...perhaps on a purchase money mortgage or lease option?...

I see this one realtor surfing all the time, so I mentioned to him that I'm looking for motivated sellers at this one particular building (because it's the only one I can afford on Maui, and it happens to produce good cash flow - plus I know the building like the back of my hand).

Seems like you are producing pretty decent cash flow and your ROI looks good as a buy and hold. 

For example - You could take $30k and put down on a income producing property and put the rest into a index fund. 

Not only did I pay off the entire loan, but I also had $40,000 leftover and a rental property producing weekly income (covers my petrol bill!).

It's curious that we aren't exploring ways to collaborate so that we can all save time and money while ultimately producing what we all seek:  quality off market leadsWhat software do you use to build your Database?