But if you plan to finish it then rent it, you would just be looking at that as added square footage, an extra bedroom or two and bathroom, which should rent for more.

also if we were to make only but a few extra payments every few years from now we'd pay off that extra interest and shorten the loan life to account for the added costs...with todays rates etc thoughts on this approach?

For example, if you are doing a BRRRR (Buy Rehab Rent Refinance Repeat), then taking an extra month to complete means that you lose 1 months rent which might be another $1200!

Depends on how trustworthy they are and their financial situation.Had a guy string me along for an extra month with words like this.

I would like to get some input from some of you experienced BP real estate investors whether I should:A) refinance 2 of the 4 rentals with a mtg for a 15 yr at 3% (currently 30 yr mtg at 4.375% - 4.875%) and let the tenants pay off the mortgage in a shorter term and take my time to pay off the other 2 with lower mtg balance.B) to sell a couple of them at current seller's market and pay off at least 2 of the mortgages with higher mtg balance which would save in tremendous amount of interest and take the extra cash flow to pay more into principal of the other 2 mtg to get it paid off quicker.C) Or to refinance the 2-3 properties for 15 year mtg and sell the other 1-2 properties and invest the proceeds in the stock or cryptocurrency market and try to pay off the mortgages in the future with the gains.  

Currently own investment wise a duplex and a SFH, thinking about paying extra on one of the loans to pay it down faster.

https://www.biggerpockets.com/...If that piques their interest, The Book on Managing Rental Properties by Brandon Turner is definitely a go to and completely worth the extra pages. 

With the market hot, you'll want to make extra sure you're running conservative numbers. 

If you have the extra cash it wouldn’t hurt.

During the peak season, this is less of an issue but during non-peak, lower-end properties that lack the amenities and aesthetic punch offered by the higher end properties suffer from the drop in occupancy the most.