Well, about 10 minutes ago, for some reason, my Browser DUMPED my Response to you. EVERYTHING I wrote went bye-bye. Hopefully, I can get my thoughts back for you ...
THere are pre-cast concrete materials as well as composite materials that are used to make 'imitation' brick and stone. In fact, because it's concrete, hence man-made, the product can be made to look like almost anything as well as old as anything. Matching is still very hard to do BUT you may get very close.
Anyways, pre-cast concrete is formed into Fieldstone, Flagstone, Brick, Granite, and so on. The Facade Products are usually FLAT on one side and 'designer' on the side that faces out. The reason one side is FLAT is because when you install it, you DON'T stack them like you do REAL stone (or whatever.) If you've ever driven around really, REALLY nice neighborhoods, have you ever seen a home where, for example, the 1st and 2nd floors of the Entrance Way are made of stone, and the rest of the house is brick? There's a GOOD chance that the Stone Facade is really pre-cast concrete or of a composite material. That's right - It has the LOOK of real, expensive stone BUT the price is that of Designer Concrete.
Now, you may have to look at your home a little differently in that it's mostly already built. If, for example, you want to use the 'stuff' I've described, would you actually have to cover over some of the EXISTING brick on the original house? Of course, you have to 'look' at it from an aestetic point-of-view as well as an economic one. A few miles from me, some of these homes are ALL pre-cast concrete/stone. But some of the other homes have part of the house done in pre-cast concrete/stone and some of the house done in brick. IF you can find 'one of these neighborhoods', maybe you'll get some ideas. At the same time, your Architect should be able to help you 'decide' if just the NEW part of your house should be pre-cast concrete/stone or part of it or part of the old and part of the new. See what I mean??? The pre-cast / composite materials are a LOT cheaper to buy and install than the 'real thing' so don't overlook it.
If you have any more ?'s, ask away. My best to ya and hope this helps.