...you need them, or wait until you need to replace a component?

I just bought a Park cassette/disk brake removal tool, because I want to be ready when it's time to replace a component. The $15 price makes it easy on the wallet (credit card).

Next on my purchase list is a tool to remove/install the threaded bottom bracket on my Trek. That's also about $15.

I think those are the only "specialty tools" needed to handle any job I want to tackle on my Trek.

Thought it was best to have those on hand before I need them. I built a spreadsheet covering the specific components on my bike, so I don't have to search websites trying to determine what's needed. I never gave bike components a second thought until I bought my Park Big Blue Book of Bicycle Repair. There have been at least a dozen different bottom bracket designs over the last 20 years, and most require different specialty tools.