How should I invest $100,000 in San Diego, CA? (May-2018)

[Jean Hayes]

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?  

2) Or should I use it to try to buy another property in San Diego?  

I honestly wish that I could remodel my hillside, San Diego bay view duplex which I bought in just a couple of years after the crash.  Unfortunately $100,000 does not buy much in San Diego and I do not have a co-signor.  It's very stressful trying to decide what's the best way to invest the small amount of money that I have, especially knowing that the decisions I make will affect how my retirement is supplemented in about 10-12 years.  I need to make the most of this hard-earned money and am open to suggestions.  

Thank you.