Generally I do the same. Sometimes I do a swap, so I sell 3 wind turbines and exchange them for a restaurant, rather than buying a random card, because then I might get a wind turbine again 😅
And when I do need population, then I do buy cards on the market, since those cards are generally cheaper in the market.
When my dcity is balanced though and I have 800 sim again, then I buy a random card again.