#1 - buying tools is never a WASTE of money.
#2 - the question isn't should I buy x? But am I buying the correct tool for the job? In this case an impact driver, propane torch, penetrating oil, and anti seize are the correct tools for the job.
#3 - stainless bolts in aluminum cases. From a hardness perspective this is an issue because if you tighten the SS fastener too tight it can pull the soft aluminum threads out of the screw hole. Also you never install stainless into aluminum dry, either use a light machine oil, anti seize, or thread locker. It is extremely easy to damage the threads by cross threading so work slow and tighten everything by hand before picking up the Allen key.
Regarding galvanic corrosion, SS fasteners into aluminum isn't ideal. SS is closer to an cathode on the scale while aluminum is an anode. When combining you want a large anode and a small cathode (as opposed to the opposite which can lead to fastener failure) so as long as you aren't going deep sea diving with your cb Honda you should be ok. Still anti seize will keep the aluminum corrosion at bay. I have pulled many old SS Allen head fasteners out of bikes and seen the tell tale white powder indicating corrosion in the hole. Same goes for brass fasteners. Surprisingly iron is closer to aluminum on the anodic scale than brass or SS so you don't get galvanic corrosion, but that doesn't mean the fastener won't rust on its own.
Edit: I was reading the chart upside down.fixed.