You are totally right. If you make quite some cycling kilometers it can be useful to invest in some tools.
I also invested in the basics a while go. The most profitable was my cheap chain breaker which allows me to replace my chain a couple of times a year. This not only saves service costs, but I pay attention to bargains from online cycling shops so I can buy chains (or other gear) with a reduced price. I always have one or more spare chains.
The one thing I find difficult is adjusting the derailler. I have often tried to 'configure' them with the screws, but somehow I never manage to make the chain go both on the smallest and the largest gear.
Maybe your derailleur alignment tool will fix this. I have nevwr heard of that one before. I'll check it out.

I know @hectorfaria1 used to post some bicycle maintenance blogs in the past.
He surely has some great tips too.

@friendlymoose