Bench Player 1:
Last year, Martinez came back from missing the 2012 season and showed that he could be a healthy player (159 games played) and be productive (111 OPS+)
While Martinez showed he can still be productive, his value in terms of fantasy is lower than it was in the past. At this point, he's primarily seeing action as a DH (he played at first 11 games last year and 3 times as catcher).
Based on position eligibility rules in the league your in, this can impact how much of an asset Martinez is. In the league i'm in , he has eligibility at first base but not catcher. While his numbers from last year .301/.355/.430 14 HRs would make him fairly valuable out of the catcher position, there are plenty of other options at first base who are capable of putting up better numbers.
Through age 34, his most similar player is Rich Aurilia. In his age 35 season, his offensive production was already going downhill .252/.304/.368 73 OPS+. He then followed that up with a couple more below average seasons before retiring. While I think the end of Martinez's career is coming sooner rather than later I still think he has another productive season or two before the offensive production falls off.
I think he'll serve as a decent fill-in if your regular first baseman has the day off but there are better options in the starting first base role. If Martinez ends up getting more time at Catcher at this point this season, that could make his spot on fantasy rosters safer. For the time being, he's on the short leash
All numbers used found on baseball-reference.com