Iain Lobb just wrote a great article called "10 reasons I prefer FlashDevelop to Eclipse and FDT". I think he has some good points, but I disagree with his conclusion. I started to write a comment... but being long winded I got a little out of control... I seem to have a habit of that lately. Anyways, please read his article before you check out my response.
First off, my info on FDT and FlashDevelop is dated. So if there have been major advancements in FlashDevelop over the past couple years then please correct me.
I used FDT within Eclipse for AS2 and loved it. At the time I was also programming java servlets so it was great to toggle between the two in the same application.
When AS3 came out I gave each of the programs a test drive and eventually went with the Flex3 plugin for Eclipse. I found it had everything the others had and more... (at least at the time).
As far as your arguments go...
1. can't argue that. that is a very good reason to use Flash develop.
2. Forcing the programmer to type "this" doesn't bother me. Its good practice and cleaner code to be typing "this" on class variables anyways.
3. Eclipse automatically adds imports when you define a variable's type. If I say "new MovieClip()"... nothing gets imported. But if I say "var a:MovieClip" then MovieClip gets imported.
4. It doesn't seem that hard. Just right click and do a refresh. But yes, you do need to specify which folders are sources. However, I see nothing wrong with this. It keeps everything clean.
5. I found FlashDevelop very annoying to switch between projects. In Eclipse if you have all of your projects setup in a workspace, you don't need to move anything around. You don't need to copy a GreenSock folder into each of your projects... just keep one in your workspace and have Eclipse target it. You can code multiple projects without having to switch anything or move anything.
6. You may have a point on the rendering speed. Haven't tested them side by side, but if there is a delay in eclipse it has not bothered me.
7. ctrl-f opens an easy to use search box in eclipse. Not to mention the ability to right click on any variable and find all the instances within a Project or within your entire workspace. Plus the ability to highlight code makes searching less common. And I love the ability to hold ctrl and just double click a function to open it up. Not sure if you can do that in FlashDevelop.
8. Sure there is a learning curve. But once you have it, I don't see you going back.
9. You can do this by downloading a plugin. Lee explains it here.
10. Buy some glasses ;). You can change all of the appearances of colors and fonts and what not by going to Window and Preferences. Pretty simple. I don't see you doing this on a daily basis. Just once and you are ready to go.
As far as my arguments for Eclipse (some are included above).
2. Easy integration with SVN/CVS
3. Code Highlighting
4. Promotes more organized workspace. No duplicate libraries. Easy to jump to different projects. Easy to find calls from multiple projects.
5. Large number of plugins available. Can customize to the nth degree.
Not sure I have swayed you. In all honesty I think they are both great products and you can't really go wrong. However, if you give Eclipse a chance and get over that learning curve I don't see any reason to switch back.