I tend to look at it in terms of budgets. I have systems set up so that when money comes in it gets routed to various accounts, including savings. I give myself a monthly spending budget (which includes buying lunch and putting petrol in the cars).
Periodically the wife and I decide to do something, such as a holiday, or perhaps purchasing an appliance. When we do this, we try to get the best deal we can, and enjoy what we buy.
We're now at the point of having enough $$ coming in the door that we cna live very comfortably, while still maintaining 5 properties. As long as we move forward every year, and continue to grow our investment portfolio (which includes assets other than property), I'm happy we're on the right path.
When our investment income exceeds half our working income (which, admittedly, is quite high), and our PPOR is owned outright, we will decide where to next.