Lyn, I think you're on the right track with the practicality and mix-and-match-ability of coordinated shades --- but it's probably important to have the few extra pops of seemingly 'random' colour for several reasons. Boredom or sameness is only one of them.
Another is when you find yourself in an environment that doesn't quite match your colour scheme --- I'm reminded of the time I ended up at a restaurant where everything from walls to chairs was blue, and I turned up in blue too. I'd have loved to have had a scarf or cardi to hand to look less like one of those fab artistes who paint themselves to disappear into them! Yes, that's an extreme example, but you can imagine, say, wanting something a bit peppier at a street carnival or a party --- not that you can't do it with neutrals, but you do have to work harder with texture and pattern for that. Colour can be an easier fix sometimes.
A third reason, which doesn't hold true for all of us but I've found is true of me, is that when I'm feeling a little off myself (healthwise, moodwise, energywise... whichever), sometimes my favourite neutrals and darks suddenly lose their appeal. Maybe it's my mood showing on my (admittedly transparent) face, but I feel like I need an extra injection of colour to appear more myself on such occasions.
Possible fourth reason: A (seemingly) out of character jolt of a different colour is sometimes exciting... for occasions when you want to attract extra attention (be it for a conference or even a bunch of old friends who you rather would see you differently rather than fall back on old patterns).
All that said, coming back to the actual garments you have here, they do seem to contain plenty of pattern interest and subtle, lower-contrast colour combinations to keep things changed up for quite a long time. Do you want to try Denise's idea and see how you get on *without* the bothersome bits? And maybe leave two or three out of the final 30 to fill in the gaps later --- which gives you even more flexibility than adding colour you aren't sure of right away?