I feel there are often times where considering a more detailed approach can help squeeze more optimal play. The base game has 4 cards:
- Train Station (4) : Roll 1 or 2 dice
- Shopping Mall (10) : Each Cafe/Bakery type earns +1
- Amusement Park (16) : Doubles grant an extra turn
- Radio Tower (22) : You may re-roll each turn
These are all characteristically different. The train station opens up the opportunity to access 7-12 roll values which may be something you want or something you very much don't want if others have cards with these values. Definitely do not buy this cheap card on a whim because you may be wasting 4 good coins that could be used elsewhere. Notice that even if you do not have cards with 7-12, you may want this one just to keep opponents with many 1-3 valued cards from getting any hits at all.
The Shopping Mall is clearly very dependent on your holdings of cafe bakery types. For what could be as little as 1 full round around the table more you, you could potentially afford the Amusement Park, and then further the Radio Tower, so again do not buy the Mall simply because it's affordable unless you feel it strongly increases many cards in your holding.
I would in general gloss over the Amusement Park and go straight for the Radio Tower typically, as for 6 coins more, having the power to retry your roll every turn is far more powerful than occasionally getting doubles which happens 1 in 6 rolls. With the ability to re-roll, consider how much more attractive that looks.