Gavin and Stacey works beautifully as an ensemble piece. Any individual character could be seen as lacking in appeal (though I have a soft spot for the tour de force that is Nessa) but the playing off one another is just great. I agree that another special would be nice but I think Ruth Jones and James Corden have admitted they're too busy now to probably do it. I have also read that a US adaptation (not written by RJ and JC) is now in the offing.
I thought MH had decided to take the 'serious actor' path in contrast to JC's continuing as a comic actor/writer plus of course all round celebrity figure. Maybe he's taking a break from tv.