Question #1 : Is Nate McLouth good enough?
Ehhhhhhh. Good enough for what? To be the 4th OF? 2013 Nate McLouth is, I guess. Overall the hitting was weak but if you plan for him to primarily hit him versus righties (with Hairston and his .270 isoSLG vs lefties) you'd be looking at a .272 / .342 / .411 line. That's fine. Plus he fielded... well he wasn't bad.
Ok so what's the problem? His offense and fielding were better last season than they had been in years. The defense is explainable. McLouth is not a CF. He played a lot of CF in 2010 and 2011 and he looked bad. The played nearly none in 2012 and 2013 and looked fair. As long as the Nats don't see him as a CFer he's fine (and why would they, with Span a lefty hitter too?)
His offense is more of a question. He really was worse in those years before 2013, but if you do the platoon thing he should be ok.
2012 vs righties : .255 / .321 / .410
2011 vs righties : .251 / .372 / .372
You see... ok. I mean 4th OF wise. The potential is still there for a big collapse here though.
The way I see it is that he isn't someone who can play everyday, but if a corner OF goes down (like this year) then McLouth + Hairston will work for a contender.
Question #2 - Was there anything better out there?
You do see a problem though. McLouth and Hairston don't give the Nats a true CFer in case Span gets injured. You can say "HA! MISTAKE!" but the truth is on the FA market there wasn't really anyone who was. Andres Torres I guess, but he's rehabbing. Frankling Gutierrez like I said, but he's not exactly Mr. Reliable. Everyone else either couldn't hit at all, or hit well enough that they should, and will, start.
Ok that isn't 100% true. There WAS a better option than McLouth and he was the greatest Nat ever, one David DeJesus. He can play center and I'd bet on him hitting better than McLouth (though also best used in a platoon situation). The Rays ended up paying him a little less than McLouth (like 250K less) for 2 years so I guess you can jump on Rizzo for a little lack of foresight. Once he was signed though McLouth kind of sat out there as the best of what was left, even considering he can't play center.
So who does play center? They can't have a 6th OF on the roster can they? Well, no so it looks like they might go down the very questionable road of having Scott Hairston be the 1st base platoon, with Tyler Moore gone, and have someone else (Eury Perez? Souza?) be the slick fielding 5th OF. Or if they are committed to Tyler Moore for some reason than the decision on a CF injury would probably be to move Bryce to CF and let McLouth and Hairston platoon in the corner. At least I hope that's what they would think to do.
I don't really like either of those plans, but the latter is a little better overall. It becomes much better if they replace Moore with an actual good 1B platoon player.
Ignorable question - "Are the Nats paying too much to for Nate McLouth"?
Honestly, if it's not enough to affect future signings, and it isn't, you shouldn't care. (and if it is enough to affect future signings you should be mad that that is the case - the Lerners should just spend. Good teams, contending teams, overpay for a decrease in variability of outcomes.
Overall I can't complain much about the deal. McLouth was clearly the best guy left on the market. He's not the perfect answer for the Nats bench, but the perfect answer no longer existed. And when you're talking 4th OF perfect doesn't matter enough. Good enough works ok.