If you're going long-distance cruising, getting the crimping tool goes a long way to being more self-sufficient in doing repairs. I've basically paid for my tool by doing crimps for neighbors at the marina who were re-wiring their boats or upgrading them. Charging eight people $15 a piece for crimping all the cables they need goes a long way to paying for a tool that only costs $150. The convenience of having the tool made wiring my own boat much simpler as well and basically paid for itself in time saved.
While I would be the first to agree that having, and using, the correct tool for a job is always best, the questions in my mind would be how often do you use it, how much does it cost, and what are "suitable" alternatives. I could just not justify spending over $100 on a tool that I only may use infrequently. In over 30 years of sailing, I have only needed to replace battery cables twice (and in the latter case, I'm not really sure the change was needed). In both cases, I bought the right quage wire, lugs, and adhesive shrink sleeves. In both cases, I crimped the lugs in a bench vise. Afterward, I used my full weight to test the strength of the crimps. I then used a DVOM to test the ability of the crimps to pass voltage. I also tested impedence. These cable passed my tests with flying colors. While I no longer own those boats, I feel certain the battery cables I installed in them are still doing the job. Yet, I have to admit that if had a friend who owned epensive battery crimpers, I would have bought him a beer and borrowed his crimpers....