Over much of the referendum world such quotas and thresholds have been incorporated in the referendum process either in a covert way or at unreasonable levels with the (usually) wilful intent of crippling the referendum process. With the result that in many referendum jurisdictions, neither the Greater London Assembly nor the Welsh Assembly would exist.
Democracy seems to get along pretty well on a simple majority. So the supermajority of 60% of votes cast required to validate the Yes vote in British Columbian PR referendum seems unreasonably high if at least open and honest.Yes had to beat No by 50%.
A common threshold is that 50% of the registered electorate must vote yes for the result to be valid. The arithmetic of this beguilingly democratic requirement is, given a 60% turnout, yes must win 83% of the votes cast. Just this threshold has neutered Italian referendums and the variant used in Scotland in 1979 produced a strong adverse reaction to referendums afterwards.
Using registered voters instead of votes cast makes Non voters into No voters and thus encourages abstention campaigns. Precisely the opposite effect democracy requires.
Thresholds can also be uneven in effect. Threshold seen as reasonable for a major issue can prove impossibly for a more specialist issue like “Dentures for old people”
If used at all, turnout quorums should be set at levels to avoid ridicule and not as additional democratic hurdles. Above all the thresholds must be obvious not covert to all voters.