There are three scenarios where paying a real rush premium is reasonable.
First, weekend or bank-holiday delivery. A biometrics appointment first thing Monday with a missing translation late on Friday is a real out-of-hours job. A 50–100% premium for Saturday or Sunday delivery reflects genuine antisocial-hours work.
Second, large bundles compressed into 24 hours. Forty pages of dense bank statements landed at 5pm with a 9am deadline next day is a real overnight job and usually means the provider is pulling in two linguists rather than one. The premium is paying for the second pair of hands.
Third, RFI emergencies with a deadline inside 48 hours. Here the value of the upgrade is real even if the linguistic work isn't unusual, because losing the deadline can cost the visa fee.
Outside those three, be sceptical. A 'next-day rush' charge on a Tuesday morning for a single birth certificate is largely margin. The same job, ordered without the rush badge from a provider whose standard turnaround is genuinely same-day, costs less and arrives at the same time.