The original Matt, Matt Holliday has been one of the most consistent hitters around for a while now. Since 2004, Matt H. is a 140 wRC+ hitter. Holliday projects out to a .186 ISO and 20+ home run player this season.
This may be Holliday's first year where it is a challenge to match his career 140 wRC+, as he is projected at 138 by the systems. His aging may be catching up with him, but he probably ages well and is good for 140+ if just a little optimistic.
In all likelihood, though, Holliday looks to be about a 3.3 fWAR player. The aging curve will set in sooner or later, and hopefully he can pull off a great season still. Just last year he was at 4.5.
Conclusion: Matt Holliday is a key part of the StL offense, even if he matches the low end of the projections.