Always do that 3Xaltitude plus 10 with wind corrections even when in VNAV and reference the airport not your miles remaining in FMC. Places like Bogota and Mexico City will clear you for this certain arrival then dump you on to the approach with you high and dry if you don't. I always put the airport in fix mode in my B757 so they can't get me by a last minute short cut. The Guayaquil approach includes a holding pattern which you won't ever do so leaves you high if you just VNAV the approach. It is always better to be down too soon wasting gas than way too high wondering if you can land.