i know it would depend on a lot of factors (event, people involved, cost, etc.) - but where do you draw the line?
for example, SIL T had nephew baptized in MI, where she lived at the time. We were living in Philly - about 11-12 hour drive from her house. We opted out because of the time and cost. (We both would have had to take at least 1 vacation day, if not 2, pay for gas, several nights in a hotel, dog boarding, meals, gift, etc. - around $700ish + 2-4 vacation days for the long weekend). ILs gave us a ridiculous amount of crap for it -yes we HAD the money and time off but that was not how we wanted to spend it.
i still think entire extended IL family is nuts for flying to Houston for Wolverine's baptism.
a wedding of a VERY close friend or relative I could justify - but travel is expensive, and vacation time is scarce.