I am assuming that you are talking about using a claw shield asn, since if you are using dual claw, blocking is only based on your weapon block skill, not dex. This depends on who you are planning on dueling against mostly. If you are planning on dueling physical chars, barbs pallys zons or melee asns, maxed block will help tremendously. The only thing is that you have to be walking for max block to take effect. Against barbs, ww asns, and zons the best thing to do is run with the control button until they are about to hit you, then release control so that you are walking. It takes some skill to get down, but my experience with my trapper was that most blockable classes couldnt kill me while I had max block. Pallies are another story though, try to tank them if they zeal, because charge is a lot worse than zeal.
Against casters however, block wont help. Against wind druids, hammerdins, foh pallies, necros, sorcs, etc it will seem like a lot of wasted points in dex, extra vita would be better. One thing I think would be better for a trapper would be to go with dual claw and weapon block. You get all the extra vita and 60% block with the ability to block casters. However, you cant max out LS and synergies until about lvl 80 iirc, so getting a high weapon block would require a level in the 90s depending on your bonus to skills.