[Syd Thrift]

While tiredness will make a player less effective on the day they play and more prone to injury, I don’t believe it has any long term effects in and of itself. The two factors that contribute the most to aging are luck and injuries. Otherwise, generally players in their late 20s and early 30s are past their prime and that’s even more the case over the past decade or so than it was earlier in baseball’s past, although 27 has been seen as the “magic year” for a few decades now.

In general, yes, you’re going to see free agent signings regress. That’s the nature of free agent signings. They’re rarely worth it from a straight value for dollar perspective; ideally you use them to fill your last remaining holes on a near championship level team. The flip side of that is that if you draft well and acquire lots of prospects via trades, etc., you can finagle 6 of the best years of a player’s career at a premium price.