These types of things are very hard to measure.
Sure, it will increase spending in bars and restaurants during the event days, but that money might just be diverted from the BC camping trip the viewers do not take.
Oh I agree 100%; where the province messed up IMO was releasing the original estimate without a fulsome understanding of exactly what they would be on hook for + not factoring in inflation, and that far out how could that estimate be close considering increasing costs for construction, time labor and materials, ongoing supply chain issues etc. That was wildly optimistic as we now see, if not an outright fool's errand.