Hold property until the end of the Mortgage, or flip now

[Jackson Sandland]

I've got a SFH that is cash flowing a little over $200 / month. $100 of that goes to property management. I bought it under market value for $90k with a 30yr mortgage with 20% down. Houses almost identical to it, in terms of style, layout, # of beds & baths, are going for around $140k in the same neighborhood. I'm considering my next move. I could:

1. Hold onto the property until the end of the mortgage. 

2. Refinance into a 15yr so I can pay it off sooner. If I'm at breakeven I don't mind paying it off sooner. If there are expenses I can pay myself back in 15 years (new roof, maintenance etc)

3. Use the equity to modernize / fix it up ( could use an updated kitchen for example), and sell it. 

I'm curious about what approaches people utilize to efficiently build wealth through real estate.
My feeling is that the people who make the most are flipping, and creating opportunities that they capitalize quickly on in the short term that add up to long term gains.  

Curious to hear anyone's experience with a strategy for building wealth through real estate efficiently. 

Thanks!

Jackson