0.4 doge worth around 10 satoshi bitcoin which is the same as the minimum bet for bitcoin betting, it is reasonable and acceptable minimum bet IMO. There is no point of betting so low bet amount than 10 satoshi except you are willing to do pre-roll. Are you trying to suggest them to let smaller bet than 0.4 doge?
The betting speed at windice with this current minimum bet is good already, if they let lower bet amount then it may affect the betting speed as dust bets usually eat more resources on the servers especially if there are so many bots betting with dust amount.