Don't forget that we're not always defending large plots of land. Sometimes we get kicked off the mainland but survive on an island. This is part of the purpose of extending SAM range and/or adding SAM warships - as far as I'm concerned, the main purpose.
Because right now - and this will continue to be the case if H-bombs outrange SAMs - a single 5-mil H-bomb can obliterate any infrastructure on an island and there's nothing you can do about it.
Allowing SAMs - if stacked up - to out-range H-bombs or adding SAM warships give you a way to defend against that. Not in a way that's impossible to attack - you can still be overwhelmed with a flood of normal atom bombs or a bunch of warships, or enemy warships farther out can intercept all your trade ships and starve your economy - but in a way that makes you a more difficult target that still requires serious investment.
I don't care as much about big land areas. Yeah, someone can do the creeping H-bomb barrage across your land, but for that to push deep inland is very expensive and I feel like if they can pull it off they kinda earned it, and the way to defend against that is for you to counter-nuke them - which you can probably do if you have enough money to build a lot of SAMs.
So I think big land areas are actually OK right now. The problem I see is small islands that currently have absolutely no defence against someone who knows how to aim an H-bomb.
That's why I would actually prefer a naval SAM ship. It should be weak or even defenceless against other ships and should not raid trade ships, but it should intercept incoming nukes just like land-based SAMs. Put a few of those in the water around your island - at a fairly high cost to do more than one or two - and your island becomes hard to nuke.