Last year's bench wasn't poorly construtcted in theory. Rizzo had all the pieces in place.You had every position covered. You had a lefty righty balance. You had a fair defensive replacement and pinch runner. Maybe there was a lack of pop and a true 3 position OF defensive replacement would have been nice, but if it all worked out it would have been great. It was just that Rizzo was relying on a lot of hope and dreams and unsustainable 2012s.
This year the Nats needed to get better and they have so far upgrading twice. Nate McLouth is a better Roger Bernadina. Scott Hairston is a better Tyler Moore. That sounds good, but looking at it critically we see some issues. Overall they've upgraded the OF without managing to cover CF. Is it because of faith in Bryce to cover that position? Or someone in the minors? Perhaps but that issue sits out there if Span goes down. Worse is that Tyler Moore wasn't actually a good bench player to have. He provided you with one, and only one, attribute. Right-handed power. He couldn't play defense. He couldn't run. He didn't get on base. Scott Hairston being a better Tyler Moore is not really all that helpful. It made complete sense for the bench the Nats had, being as awful and power-lacking as it was, but it makes less sense for this year.
Of course if the Nats can upgrade with a better Chad Tracy and Steve Lombardozzi that will help cover up carrying a one-note player. Is there a better Chad Tracy out there? Yep. Eric Chavez. Problem is Chavez wants to play and there isn't a good place for him. Zimm isn't going to sit that much and Chavez is also a lefty making platooning with LaRoche very unlikely. After him the only lefty bats better than Tracy would be Lind and Loney, both who should find starting roles somewhere. That makes the most likely corner guy signing Jeff Baker, but he is a righty bat and really only should face lefties. This would give the Nats two players like that limiting the bench severely for late game hitting.
A better Steve Lombardozzi is also an issue. You're not going to find guys that can hit and field in the middle infield. If they exist they are starting. Instead your best bet is finding decent gloves who aren't terrible at the plate. Mark Ellis might work but he hasn't really played 3B or SS. Brian Roberts wants to start, is a gamble and is only a 2nd baseman. Ramon Santiago is terrible at the plate but he can play all the infield well. Given the Nats have pretty decent defense in the infield I guess I'd default to Ellis but it's an imperfect match.
Let's think about some scenarios:
McLouth, Baker, Chavez, Ellis - need to trade Hairston in this scenario and assumes you can get Eric Chavez, but that's a very solid bench, ignoring CF coverage.
Likely all FA
McLouth, Hairston, Baker, Santiago - only one LH bat hurts balance (Santiago is a better lefty bat than right but that doesn't mean he's a good lefty bat).
The all gamble bench (well not McLouth but he's set)
McLouth, Youkilis, Gutierrez, Espinosa - hey if it all came together that's a hell of a bench
Most likely right now it seems
Baker, Espinosa - a lot like the one above except making a huge gamble
that Espinosa can hit at all. If he can it's much better than Santiago
but who has faith?
There are other options. Somehow get rid of LaRoche. Sign Infante and make Rendon your MI bench guy. But I don't see anything crazy happening unless part of a larger deal.
If the discussion above sounds too negative to you, you're right. The question isn't whether the Nats will have a better bench, it's a question of how much better it will be. That can't be hammered out until the work is done. Until then though, we'll have fun arguing about the margins.