ActionScript 3.0 :: Flex Embedding Images And Dynamic Variables

I'm having some trouble with loading images for my tiles in a small game I'm making. It's isometric and tile based. I have two questions: I have a class called MapTile which is for each tile in the map. Each tile is made up of 1-9 blocks stacked on top of each other (like Final Fantasy Tactics). For example, let's say there are 4 different kinds of blocks: grass, dirt, stone, and water and they all have different images. I was considering embedding only the images needed (so if a tile is just grass on dirt then it would only embed the dirt and grass images). Will this actually make the game faster and smaller or is it worthless? If it's worthless then just ignore my next question.I'm trying to embed my images dynamically as stated above. So I have an array called loadedTiles that contains the class names of the tiles that have been loaded so that I don't embed the same thing twice. And I try something like this for embedding new images:

Code:
var sourceT:String = "../../../lib/tiles/" + tilesList[data[i]]["image"];
var nameT:String = "block" + tilesList[data[i]]["id"];
[Embed(source = this[sourceT])] var this[nameT]:Class;

[Code]....