Everyone has their own preference to which currency to use, but the idea that smaller bets increase your chances of fulfilling the wagering requirement is a common misconception.
I have to admit that I used to think the same, but mathematically, that’s not true. The chances of completing the wagering requirement depend on your bankroll, the game RTP and, of course, your luck. The same applies to bonus buys as well.
Bet smaller means you will have to bet more times and in long run, difference is not too big between bet small and bet big. Because the most important thing is bet in many times to reach the required wager volume, and factors that affect it are things like you already mentioned: bankroll, RTP of games you played with, and luck factor.
Skillful gamblers and participants in wagering contests will know well about these factors, choose good games to play but during playing and wagering time, they must depend on luck factor to defend their gambling capital and achieving wagering requirement.
I think the important distinction is between bankroll longevity and the actual probability of completing the wager requirement.
Betting smaller doesn't increase the mathematical chance of completing the requirement by itself. It mainly allows your bankroll to survive more spins and reduces the impact of individual losing bets. If you have a limited bankroll, that might still a reasonable strategy.
For ex. the wagering requirement of $1,000, betting $0.028 (base on @Renampun) means you need roughly 35,700 spins, while betting $1 requires only 1,000 spins. The amount wagered is still the same.
And that's right that the total wager volume still has to be reached. RTP, bankroll, bet size, and luck of course, determine whether you survive long enough to get there.
