I hope you welcome (some of) these ideas based on my initial experience with 1.1.2 Free edition:
Inspector could also offer spinners for adjusting integer properties e.g. GridData.hSpan, where +/-1 etc. is common
Content Pane's popup align images could have tooltips showing which property and value they would set, or they could highlight same in Inspector
Inspector's combos could expand to show all items if possible (as with all popups, you can't do much else on screen while they're there, so use the available space for user's convenience) (choosing named colors is fiddly)
Do named colours relate to swatches in 'Color' dialog? I guess you can't add tooltips to the (Windows) swatches, but could you add mini swatches to Inspector's combos?
right/left cursor keys could expand/collapse complex properties in Inspector
(optionally?) show all inner borders of a GridLayout in Content Pane
delete Control Tree items from keyboard
merge TabFolder and TabItem into a single virtual composite (you can't really have one without the other) (and SashForm doesn't need SashItems)
could layout-less composites nevertheless have a 'layout' property, with a pulldown list of alternatives? from the designer's point of view, layout is essentially a (complex) property, not another control