Be very very careful about joining the TWU, read the fine print carefully. When I worked as a lawyer I represented several people who wanted to cancel their membership. The TWU had some nasty provisions about that and were ruthless in pursuing them.
As to paying for ICUS, I have done it twice. The first was at the conclusion of my instrument rating when I realised that I only had a rating to learn. I bought some hours to consolidate the training and to get a feel for "real life" IFR. I still consider it the best money I have spent on training.
The second occasion was just prior to the first instrument rating renewal when I needed to get back to speed on flying a twin. Again, I consider it money well spent.
The rest of my entries under ICUS in the logbook were getting time on type prior to being turned loose on an unsuspecting public by my employer.