Gt cityYou're very welcome.
In my humble opinion, this would be a mistake. Unless you are backed up against a wall (Say, like having your repair base awaiting items and being unable to repair your planes). Greenies are very hard to come by. The special code given this week does not happen every week. It's only special occasions.
Land is what you are mainly wanting to concentrate on. The more land you have for the airport and city side, the better off you will be. Every week, they give out 3 greenies. Every time you pass a level, you obtain a greenie. You can also buy them every other week if you so desire.
DO NOT waste them speeding up, or bypassing obtaining items. That's that joining this forum will do for you. Someone here has Flight Goggles, and they would be more than happy to become your neighbor and gift them to you... For free. Or, you can find the destination you need to fly to in order to obtain them, and get them that way. Either way is better than spending greenies to speed up the opening.
Another suggestion, before you upgrade a building, look in the store at the building you need to upgrade next. There is a small information button now that will tell you what that particular building needs before it can be opened / used. Then look around at signatures. Much like Flight Goggles, I'm sure one of us will have the item you need. Maybe more than 1. Sometimes you can get all items in one day. Other times, not so much (Such as when an event is going on). This way, you don't HAVE to be tempted to spend greenies to upgrade.
Question 1 - This depends on how you want to play the game, and how fast you want to get there. It's a personal decision. Many people will tell you their ideas of the best way of doing it, but it still depends on how much time you have to play, how much you play and how you play. Although, keep in mind that certain planes need certain level hangers, much like certain level repair bases. You can put any plane in any hanger, but if it's not the right hanger for it, it may take a lot longer to load then it would if you had the right one (If that particular game feature is still present anyway).
Question 2 - In a word, yes. It is worth it. You can buy adventure maps, and many other special items through the Airship Store. Adventure maps allow you to fly to various, "Off the normal flight destination grid" and obtain special buildings, as well as gold and silver tokens. Which can also help your gaming immensely.
Hope this helps you somewhat to decide what you would like to do, and how you want to get there.
Thank you again for the awesome thoughts and advice. Have been going along rather haphazardly it would appear.... I have kind of binged on this the past 10 days, so playing with abandon sort of.
Will endeavour to become a better participant - still working through this forum - yes, people are awesome!
...if that helps you figure their value any better. Land becomes exponentially expensive in coins and after the 200,000 coin expansion, waiting for the land sale (going on currently) to pay 7 greenies, then later 10 greenies each really multiplies quickly. 
Consider how much fuel you have left when you fly all your planes out at once, if it's enough for another plane to go out, you probably could consider upgrading the control tower. I find for a long while in the game, there is no need to have any hanger higher than a green (lvl 2) as you will be flying mostly turbos and jets, and upgrading to anything higher will be a waste of resources. On my android I am level 34 and have 4 blue (lvl 1) & 2 green (lvl 2) hangars. I fly 5 turbos, 1 jet and generally have just enough fuel when all flown out at once, depending on the choice of destination of course.
ItsRalphy
skiv
Wired Parrott
Ten33go