Generally speaking, baseball players in their mid-30s aren't supposed to be great, but Curtis Granderson was last year. It was his second season with the Mets, and he was coming off a just-decent season in 2014 and an injury-shortened season with the Yankees in 2013. There was a track record there before all of that, but there wasn't any guarantee that he would be very good last year.
Granderson's season went about as well as anyone could have hoped. He played in 157 games in the regular season, and over 682 plate appearances, he hit .259/.364/.457 with 26 home runs. That's a very respectable home run total these days, and when the offensive production was combined with his plus defense in right field, he was worth 5.1 fWAR.
Just how much of that change can be attributed to where he hit in the batting order is debatable, but after splitting his time between the leadoff and cleanup spots, among a handful of others, in 2014, Granderson hit almost exclusively in the leadoff spot for the Mets last year. Considering how well things went, it'd be hard to imagine the Mets changing things up in that regard, particularly since there's plenty of power throughout the rest of the lineup.
Granderson enters the season as the Mets' everyday right fielder again, but with the crowded, Yoenis-Cespedes-included outfield, it's conceivable that he could see a bit more time off against left-handed pitching. If Michael Conforto's reps in right field in spring training happen—and they go well—that might make Terry Collins more inclined to use an outfield of Cespedes, Juan Lagares, and Conforto against some left-handed starting pitchers.
Even if that's the case, though, Granderson should get plenty of playing time. If he can even come close to matching what he did last year, the Mets should be in good shape. The starting pitching is rightfully getting all of the attention right now, but the team's lineup should be pretty good.