Responding to a destination-wedding invitation is a bigger decision than a local one. You are committing to a flight, three nights of accommodation, and $1,500–$4,500 in total costs. The couple needs your response quickly, and you need to think it through.
The answer to "should I go" is almost always yes if you can afford it and clear the dates. Destination weddings are memorable because the guest list is smaller and the programme runs longer. But money and logistics are real constraints, and no is an acceptable answer.