Yay, I hope you can save some tax $$, Sylvie! OK, I'll try to address all the questions quickly:
1) I like bright colors - If you wear a lot of bright clothing, gray boots could be really nice. IMO they help make the brights a bit softer/more elegant.
2) Is it hard to get pull on boots over skinnies? I haven't had trouble - I usually just tuck my skinnies into my socks, and they hold the jeans in place.
3) Can I wear laceups over skinnies - I sure plan to do so! One of the reasons I love laces - adjustable shafts.
4) I've told myself I can replace my other black ankle boots when they get down to <$1 CPW - how badly do your others need replacing, and how much do you love these? Can that shaft fit over skinnies, or would they only be for dresses/skirts?
5) I do have a lot of black shoes already - In that case I vote for UNblack.
Personally, I think I vote for #2. They are a color you don't have and could be the flat black riding boot hole alternative, since the soles are nice and dark and they are still neutral. I do like the colored ones also, but I just usually prefer colored shoes with more neutral outfits.