I'm probably going to make a holy PVP and a holy PVE spec for my paladin. I do wish "dual specs" covered more then just 2 for us hybrids (I like to tank as well, and sometimes even play ret), but at least 2 is an improvement.
I respec for arena, but I won't spend the gold to respec simply for battlegrounds. However, sometimes I respec for arena, then I'll stay PVP spec until the next raid. Doing a few battlegrounds as a true PVP spec is more fun, you die less, feel more helpful, etc..
Personally I go 51/5/15 for PVE, and 49/0/22 for PVP. Theres some subtle differences in the holy tree between talents (mainly dropping improved wisdom for unyielding faith), then I skip kings and pick up divine purpose and pursuit of justice. It sucks they're shifting the ret tree around next patch, hopefully it's still viable to pick up divine purpose, because in many cases I'd be dead without it.