Maybe our idea of unrealistic is different. I think every board is going to have some hopes of acquiring good players. We arent the biggest market but we arent exactly the Rays. There is always a big bump in payroll with the opening on a new stadium. Even the Marlins spend money the year they open a new stadium. Lucroy isnt going to get 120+ million in free agency like the others you mentioned. I would see it a lot like the Uggla trade.
The Marlins may have spent money, but they didn't spend prospects, which is what would have to happen for us to get Lucroy. I don't think anyone believes the Braves aren't going to spend money in the offseason. They will have a lot of it available and unless they give out some budget-crippling deal it's probably not going to set back the rebuilding effort.
What's frustrating about reading all of these posts talking about trading for Lucroy is that they don't seem to contain any reasoning beyond "well we have the prospects to do it and the Johns probably want to make a splash for the new stadium." There are multiple contenders who could use both a big bat and a catcher. We are not going to be competitive next year*. Therefore, Lucroy, who is on the wrong side of 30 and a catcher and only signed through 2017, is more valuable to a contender than he is to the Braves. Therefore, if he is available at a price the Braves are comfortable paying, there is likely a contending team who is also willing to pay that price or even a bit more. Conversely, if his price is so high that no contender is willing to pay for him, it would be absolutely insane for the Braves to turn around and pay it.
I get it, rebuilding and being terrible isn't fun to watch, but good lord try to be patient. Trading legitimate prospects for a 30 year old catcher with 1 year of control when you are the worst team in baseball is exactly how you muck up a rebuild and end up like the Pirates or Royals.
*You can debate this all you want, but I have yet to see a scenario where we're competitive in 2017 that doesn't rely on the Braves signing 2 of the top 3 free agents in the offseason
and trading for Lucroy
and Albies/Swanson both having breakout rookie seasons
and Folty/Wisler/Mallex/Inciarte/Blair all taking a major step forward
and the Braves cobbling together a decent bullpen.