Imo info about buyback is too hidden when spectating. You could say that it's even too annoying to get this info in game as well. I got some pics which shows almost everything what you need to solve this problem. Also added few other propositions:

gi2fnEV.png

Gems on heroes icons which show ult status are useless. Imo much more convenient would be to give info about buyback there, since when spectating you also get there info about hp so it would make sense. But you could have them both there. Made 3 options which could be reasonable solution.

Flashing gold icon could be useful ingame too not only while spectating.

Courier is also hidden too much. You don't need icons to use courier because you are not playing! So courier status is enough. Also icons have to be different to reflect sides (that bluish icon supposed to be dino courier from dire). Also something what is important clicking on the icon would select the courier so you could see what he have even when he is dead. Dino icon could be used ingame when playing on dire side as well. Makes too much sense.

Glyp info imo should be seen always for both sides like couriers.

XP bar color coded would make it easier to remember those colors on heroes, so it will be easier to see who is where on the minimap. Could be useful ingame too not only while spectating.

Mouse hover info makes too much sense to not add this. At least for spectating.

Ward always on quick buy would be super helpful on support heroes. One of few ingame suggestions specific that isn't related to spectating.

11IXfIP.jpg
Additional and optional info tab. Imo there is enough space to support up to 2 of those tabs.


Other suggestions:

Alt click on hp bar and buffs
http://dev.dota2.com/showthread.php?t=137558

Turning off all windows at once
http://dev.dota2.com/showthread.php?t=137554

Steam Market Update
http://dev.dota2.com/showthread.php?t=136313

More info after a match
http://dev.dota2.com/showthread.php?t=118125

Soundtrack release
http://dev.dota2.com/showthread.php?t=126552