We recently got orders and had planned on renting out our house however after taking into consideration that age of the home, we decided selling would be in our best interest.

This can be dealt with in a couple ways including accessing its value (age, condition) compared to other commercial properties that have sold in the same area or using the mid point cap rate.Any large commercial broker familiar with the area of the properties should be able to provide cap rate range for each property.Commercial property valuation is so much easier than SFR to quad.I have seen sellers try to use a projected NOI but this is bogus. 

Age old debate diversify vs economy of scale.

@Justin HerringtonSlick acronyms aside, buying smartly and forcing appreciation is an age-old strategy which can work almost anywhere.

Hello, I'd like advice from experienced investors on how I should invest $100,000 in San Diego, CA.  1) Should I use it to upgrade my aging, dated, duplex in order to command slightly higher rent?  

Average age of death is currently 78.7 years and the baby boomers range from 1946-1964. 

If a deal just looks "OK" I  will still play with the numbers to see what my break even point is and what would have to happen to get there - if there are too many red flags then I walk away - there are still many other factors that I will look at such as location, age of property, type of property , local comps, ARV , potential add-ons  and other factors that would affect the cashflow and/or resell value.  

I have several AirBnB properties in Dunedin and find that it's a mix of vacationers, people moving to the area for work or retiring, and people visiting aging parents. 

Me paying it off in my ideal time frame (8-10 years) coincides almost exactly with him being between 65 to 70 (ie retirement age) so I know I could make more money by delaying the payment, but I would rather take care of the man who has taken care of me my entire life first!

Chris, unless you are at the retirement age pulling funds from your 401k will be considered early distribution, which will result in taxes and penalties (both on state and federal levels).