Looks up close and great from the distance, it does not seem worth going in, especially if you do not have much time in Sintra
It makes sense to start here very early with the Sintra Tour. If not a big crowd, then the "Palácio Nacional de Sintra" is definitely worth a visit. But I would not wait for a long time.
Worth seeing, but the emphasis in Sintra, I would rather put on the Maurenburg and the Palácio Nacional da Pena. This one is well busy in terms of time and resources.