Have played the Vindicator all the way up just isn't really worth it honestly. The first couple of levels it gives you the nicer abilities of the class. Higher up they are not impressive enough to lose the spellcasting potential as a full cleric. The first level of it is nice enough. You add the number of dice of your channel to your AC until you are hit for one channel. So figure by the time you hit this class your channel die is at least four or five. That's 4 or 5 points to your AC a big step up for one channel a day well worth it. The nice thing about the ability is you don't have to be using the shield to get this boost. You could wear a buckler or just carry a shield on you back and you get this.
Yeah it's not a very good prestige class. In the RotRL campaign I'm playing in my character is a cleric 8/holy vindicator 6. I've felt the HV levels have mostly been worth it, but I built my character from the start to take levels in HV. I do think however taking some levels in it is a better alternative to taking levels in fighter if you can hold off having the weapon and armor proficiencies until 8th-9th level.