we have 3 days in lisbon - worth it?
When I was in on a 7 day trip to Lisbon in 2019, I calculated that it wasn't worth it for what I wanted to see.
You need to check if there are enough sites covered by it that you want to see to help you decide.
No.
Buy your admission tickets in advance. Almost all "attractions" offer a discount for seniors (if you are eligible).