I will put in my two cents... I love ADE, by the way... Great program...
(If these are duplicate requests, please ignore them accordingly...

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1 - Seasonal output routine options.. I will explain... I am placing a number of vegetation guid's, quite a few to populate the airport... most have all seasons in the library list... Would it be conceivable to make a routine or wizzard, where you place your trees from the library in summer guid's, and you have the ability to compile the scenery in all seasonal variations. Meaning: it outputs the scenery with your summer trees, then can 'change' the guid for the trees you placed, to have the corresponding seasonal guid, and make 4 or 5 output bgls, with the respective tree's season guids in each one... If FSX is not going to change seasons for you, because it has a guid for each season... one would have to create and place 15 to 20 different tree types and sizes for the scenery, and thus do this 4 or 5 times from scratch, placing all trees every time because there are guid's for all trees all seasons...
So, would it be a pain for you to incorporate a way to do trees/vegitation, where you place the summer guids, and ADE can output whatever season bgl you select, by changing the guid for the Maple 10m to the one for the Maple 10m sp, and Maple 10m fa, etc....???
Currently, I made one set of trees and vegetation for the airport, looks great, but I cringe at the fact that I have to do the vegetation all over again for each season...
I hope this makes sense...
2 - (this has already been suggested, but I second the suggestion) that an ability to create a line of models as a said distance would be swell, a great way to place lights, lamps, etc with precision......
3 - when freezing or locking objects or sets of items, that they are no longer able to be effected... i.e.; currently, I lock the aprons... and models i have on the aprons dont get selected, as trying to select them keeps highlighting the edges of the apron... the apron doesnt move, but it makes selecting the models difficult, because it keeps trying to select the apron....
4 - Ctrl+V works as a 'paste at mouse pointer location', instead of right mouse clicking and having to left mouse select paste... This will make placing similar models and objects go sooo much faster... I think this is what the previous person who mentioned a 'clone' option might have been thinking of... copy/paste works, sure, but perhaps could be streamlined a little...
5 - Position makers not be so 'thick'... I know this is for visibility, but when zoomed in for some detailed positioning, it was difficult to get alot of accuracy when lining some things up with current scenery edges, etc...
Some great ideas already posted by others...... ADE is a great program... I am really enjoying using it for most of the layout work with my sceneries... Thanks for consideration of these items, and definitely Thanks for making ADE....