I agree with most of the other posters. Matsui is probably not worth keeping unless you're in a dynasty or deep keeper.
Here's a good way to look at it: consider the number of keepers you reserve and consider them rounds in your draft. If you keep 5 players then a player is only worth reserving if his value for next year justifies drafting him in the first 5 rounds. Of course you have to make adjustments if you're required to protect players and your lineup sucks.
As for Kaz, a while back, on the WFAN, Duquette pretty much admitted that this was the plan for next year. It makes sense because Reyes is the better Shortstop. If you watched Kaz a lot and you're familiar with his range and his deficiencies it stands to reason that 2B will play to his strong suit. I think he can become an excellent 2B and fantasy-wise he could be very good because of the offensive derth at the position.