I also haven't been able to experience 1000x wins from the sweet bonanza, and looks like it will be a very rare to win. but, if i remember, I can just get half of it.
I would suggest you to try the Christmas edition of Sweet Bonanza than the original Sweet Bonanza.
As per my experience Sweet Bonanza X'mas is better in giving big multiplier.
If I remember it correctly, I have ever hit more than 1,000x multiplier few times with the buy feature ofc.
But I have never hit it in the Sweet Bonanza, but for sure its all about luck as maybe my luck is better in the xmas edition than the original one.