I have one, don't make as many long journeys these days but I get my money's worth. Just do some sums, you'll probably find it pays for itself.
My Dad had severe hearing loss and he got a disabled person's card, mum never went on the train in her own, without her he couldn't hear announcements.
The senior card seems to have fewer restrictions.
Our local area ( and I know other areas too) have reductions if you have a bus pass. I use mine locally for trips locally that start after 10, I get child fare which is better than senior Railcard. So when my senior card runs out, I don't get another one until I am going to take another longer journey or one out of the area
Both the cards I've had I've asked for as presents, my first one was for my 60th birthday from mum, a 3 year one, I got it just before I made a long journey. Then when it ran out I asked for another one from my children and again I waited until I was going to take a long journey