I've been following a similar approach for a while. In bash, I have `HISTCONTROL=IGNOREBOTH` activated (or `setopt hist_ignore_space hist_ignore_dups` in zsh - most shells have an equivalent setting), and I just prepend most commands with a space. So only the more or less important stuff ends up in .bash_history or .zsh_history. This has the added nice effect that I don't accidentally trigger something destructive when I browse through my history.
I also spend most of my online life in incognito windows, at least for sites that don't absolutely require a login. This keeps my browser history clean from all the disposable pages that I only visit once, and I take care to do only the more meaningful stuff in a regular browser window.
The history file has ALL the lines prefixed by space. I curate it a lot, with most frequent/recent commands near the end. And I add a lot of comments to the file so things are easily searched. And search for things, for example /rsync to find the rsync quick backup snapshot lines so first comes one with -n to check what it would do, then if it looks OK I press 'n' (vi mode) and get the same line without -n, or another 'n' and I get the same without -n and with --delete.
I also spend most of my online life in incognito windows, at least for sites that don't absolutely require a login. This keeps my browser history clean from all the disposable pages that I only visit once, and I take care to do only the more meaningful stuff in a regular browser window.