Also, there is the opportunity cost of having your money in land when you could have it in a cash-flow producing asset.  

I would greatly appreciate thoughts on the following...I am an amateur investor with 5 income producing properties.  

You need to make sure that what you borrow the funds for produces enough cash flow to make the quarterly repayments.

That's not the sole issue and the 2300 noi is great - - if you can keep 100% occupied and the PM costs don't kill you.Ask yourself, why is the MFU producing less profit per door than the SFR? 

If you buy in a neighborhood with poor supply and demand fundamentals and no history of appreciation and hope that the neighborhood will turn the corner and start appreciating at a rapid clip the day after you close escrow, then yeah, that is speculative for  sure.Also, don't forget about forced appreciation ... this happens in the short term and does not depend on the market to produce it ... study how flippers make money to understand this ... you don't need to be a flipper either, you can buy, fix, and hold in a similar fashion.

Use the proceeds from the sale to do those improvements, and buy one income-producing investment property. 

Due to my background in engineering I could produce plan and elevation drawings myself.  

It is often time consuming and expensive - all while the land is usually producing zero cash flow.

I've been able to purchase them well below market value and modestly rehab the units to produce top rents.

Keller says if you keep the pedal to the medal in your lead generation model you will continue to produce even when the market shifts.