Decision Advice: Sell Vs Hold

[Tyler Brown]

High level decision making question: how do you decide when to sell/1031 vs hold?

I have a Vegas 4 plex that has appreciated and cash flows well. Purchase price ~$425k, owe ~$320k, PITI ~$1600, rent ~$995 per unit. Similar buildings now selling for $550-600k. Current cash flow ~$1k monthly on a 3.5% 30 year am.

Best case with sale, take ~$250k proceeds in 1031 for down payment on another property up to ~$1mil at around 5-5.5% depending on sale time and rates or sit back, allow continued appreciation, cash flow and see how the market goes? 

Surely, this is a common (good) problem for experienced investors. Any advice?