Interesting thread.
I have had a fourline green wrasse in my display for a couple of months now.
Personally, I don't know what size tank it would be "too small" for since it is a very active fish. I don't find mine to be secretive at all, more often than not it follows my every move hoping that I'm going to feed it. When it isn't watching me, it is searching every nook and cranny in the tank looking for something tasty.
It is territorial, when I added a yellow watchman goby the wrasse nearly killed it before I could get it out of the tank and into my refugium.
IMO the fish is quite a bit more attractive than the typical 6 line and I would recommend them for anyone interested in a small, active and interesting fish.
All that being said, my fish is about 3.0" lip to tail and I paid a whopping $39.00 for it at a local fish store, so they can be had for less than a hundred bucks; I'm afraid you are another in a long line of folks who have been overcharged by that particular store. So why not just keep it? It's an awesome fish.
EDIT: as a matter of fact, this fine website sells them for $39.99 +shipping for a 2" fish when they have them in stock (which they don't right now)...