One of the great things about this game is that everyone can set their own guidelines (cheaters aside, they don't count). I imagine it ranges the entire spectrum with someone like Fletch with an iron-clad no buy rule (and iron-clad discipline and patience to match!) to maybe someone like me who tends to be impatient and a pretty free spender. However, I'm not debauched and I have set rules for myself as I want to accelerate things, not simply buy my way to success (I've always built my own cars which is more gratifying to me then just buying one). Here are my rules:
(1) Buy only gems, never coins, treat or eggs - except for the very low cost elemental eggs that you can buy with coins.
(2) Stick to a budget of $4.99 a day, maximum $9.99. It's really inexpensive entertainment as its the only thing I spend any money on right now.
(3) Have enough discipline to stay on a 1 hour breeding cycle and occasionally let it go 2 hours (pathetic, huh Fletch?).
And that's the structure that provides me with the most enjoyment. Your mileage will vary. LOL
Poppy