Depends how often you go there. We visit up to 10 properties every year, some we go to regularly to walk around the gardens, probably use the tea shops. One is one of our lunch stop-overs when we head off to see DGC in Yorkshire. You need your ticket to access the gardens and cafe's; anything is better than a motorway service station.
We also belong to the Historic Houses Association (HHA) and English Heritage. As you may gather we are heritage junkies.
We also like supporting them even if we do not visit because, disgruntled (I love that word!) as I am with the NT, they, with the other two do so much to protect our countryside from the depredations of developers.
We have seen in our area that the Green belt, once thought to be sacrosanct is constantly having large chunks bitten out of it under the cry of more affordable homes, which the houses then built on it are not, because the Green belt is under the care and supervision of the government and local authorities.
The NT also do much to encourage ethical farming, though even with that they have a tendency to over-zealousness.