I think that CPU load figures from Activity Monitor are not necessarily a good guide to performance.
First, remember that “100%” represents approximately 100% use of one core of your machine — and almost all of you have four or eight of those. One design aspiration of Tinderbox is to use the power your machine has, not to leave it lying around idle.
You’re right, though, is suspecting that maps with hundreds of notes will suffer some performance penalty when repositioning notes. One of the big changes in Tinderbox 7.5, in fact, was a significant performance boost when dragging items in complex maps. Still, there’s a lot going on when you move items.
I don’t think badges are likely to cause any observable performance issue at all.
I can imagine three ways that adornments might cause performance issues. If your Mac were very old, I suppose that the GPU might not be up to compositing lots of adornments. I don’t think any Mac that could run Tinderbox today would have that problem. Second, there might be some unforeseen issue in the map guides that’s causing trouble; the guides treat adornments specially, and you may be doing something that others haven’t tried. Third, I suppose that smart adornments could create more computational load, though I don’t really see the mechanism.
Finally, one guiding design principle for Tinderbox does contradict contemporary practice. We place a higher priority on getting complex work done than on surface aesthetics and experience; if we need to choose between frame rate and doing some useful computation, we’ll do the computation. When it’s a question between looking good and doing work, we’ll do the work. Still, when things get too ugly or too slow, we’re amenable to picking things up now and then.