As has been mentioned above, its a very slippery slope, you always need something else . .
Just bought myself a brake pipe flaring tool, 30 quid for something I'll probably use every 5 years or so!
Unlike just about everyone else on here I have taken a different approach to buying tools. A week before I start the task, I research what tools I need, then I goto an online auction site and buy the cheapest version available (usually some unheard of Chinese brand). I use them to do the job and if a part fails I nip over to the local Halfords and replace that component only.
Disadvantage is that you have many plastic cases holding things, instead of a single one, but that means I don't have to lug a huge case up and down stairs.
So far a single 17mm socket has failed (Draper value) while trying to get off a caliper bolt with a long breaker bar, so I'll stick with my cheapo kit until I can afford something prettier.