This is good, but I will miss the previous colourful defaults.
They aren't going anywhere. When you start Inkscape for the first time, your current style is empty. And when it's empty, all tools use their own style regardless of the setting. Which means you still get red circles, yellow stars, etc - up until the first time you change someone's style. That colorfulness was intended for novices, and novices will still see it at first. If you want the shapes to be always colorful, it's a matter of a couple of clicks to change the setting for each tool.
Can someone think of a way of providing the usefulness of this change while providing the colourfulness associated with the old behaviour?
I think I thought about that, see above :)
Should we have more prominent paint palettes like most drawing programs (gimp) ?
Of course. It's in our stack since forever. Just go ahead and code it :)
Along the same lines, we could make the star default to slightly rounded with a hint of randomization: something a little "fun".
I'm not sure... this may be _too_ cheerful for a poor novice :) But anyway, all shape parameters' defaults will be settable in prefs - that's next in my list.