Reply to Screen Real Estate question on MBP 13"

Okay, so I just bought a new MBP 13.3 inch and im kind of regretting not going with a 15". It does have the thunderbolt display out, but im not dropping another grand on a 27" monitor. So when running 4 decks in traktor I get about 3 tracks worth of browser at the bottom.

So my question is if I buy a ordinary LCD monitor, say a 23". Will this actually increase screen real estate... or wil it just blow up my image that I have on my laptop now, in other words, be a direct "mirror"? Anyone have any experience with this?