I feel the same way, for the most part - against the Spanish I've mostly played the Keres (Chigorin with ...Nd7 and ...ed4) and the Marshall, both of which are pretty forcing and challenging (although admittedly the former might not be entirely sound), and against 1 d4 I'm playing a repertoire pretty similar to yours. 

I've played the Breyer a decent amount in blitz and rapid (just to mix it up), and yeah, along the lines of what you said it's probably especially poorly suited for those time controls, because White's play tends to be much easier.

And re: the QGD, like Jan Gustafsson said in the intro to his Vienna series, there's not much reward for being good at the QGD.

Fair enough - thanks for the info!

Thanks for the replies!

Re: to the winning chances thing, I probably should have suspected as much.

I did actually play (read: aim for) the Marshall for a while, but I almost never got it on the board (once in ~30 Black 1 e4 e5 games OTB), and when I met 8 c3 online I often did terribly, because my opponents just knew more than me (because I'd barely put any time in, given no one was playing it).

Yeah, pretty much everything chess-related Svidler does is excellent, I need to watch his Archangel series at some point. I asked about Shirov because I know he recommends 13...Bxf3, which I'm interested in, as opposed to Svidler's 13...ed4.

Finally, the insight into what lines White players are choosing is appreciated. I also like the 10 a5 line for White, Isa . 

I've played 5...Be7 etc. for a decently long time, so I have a more or less reasonable idea of the frequency of the Exchange/5 d3/5 Qe2/whatever else vs. 5 0-0. However, I have almost no experience with 5...b5 - Eric, what's been your experience with people going 5 0-0; do you get the main stuff with a4/Na3 (or a5, as above) a lot?

Thanks again!

My attempt at answering (mind you I'm just a ~1900, so ymmv, but nobody else is saying anything, so I figure some answer is better than none):

1. I believe this greatly depends on a huge number of definitions in that sentence, ie "knows what he is doing", "realistic chances", etc.
Of course if White is perfectly prepared in every line up to move 30, there won't be a lot to do; but Black has several paths to take even within the most critical lines, and while they may not objectively equalize, it is very unlikely that White actually "knows what he is doing" in all of them - unless you're like a 2600+ GM. 
Eg if you take the mainline position at move 18 (after 13.Bc2 ed4: 14.Nbd4: Nd4: 15.cd4: Bf3: 16.gf3: Qh4 17.Kh1 Qf6 18.Be3), now Black has picked between 18. ..Ra8, 18. ..Nf4, 18. ..g6, and 18. ..c5. Who is going to have deep prep on four different branches at move 18 of a sideline?

Then of course there is always the question how ambitious the White player will be - if he just wants a draw starting from the onset of the game, it's quite possible that you can't do much about it, but that's the case in pretty much every opening.
You could ask the same question about the Marshall.. which I do think gives very realistic winning chances if you are better prepared and/or White is challenging you in some fashion, but of course if White wants to he can pick a variation where you either have to enter dubious waters or it's just a dead drawn endgame; but how often does this happen? Either White tries for something, then it won't be an issue, or White is vastly lower rated, then he won't know what he is doing.

2. Not that I (or anyone?) know of. Svidler gives 15.f4 as the critical line, but also notes that it's being played in Correspondence semi-regularly and Black holds his own. He said he didn't find complete equality, but then again neither did he in his own mainline, so it appears to be as valid an option as any other. Perhaps in practical terms this is easier to deal with for White (either than for Black, or than the mainline)? 

3. No idea, never saw it. The only comment I can leave here is that I've seen a lot of poor reviews of his DVDs in general; that they're underprepared / lazy / badly made / etc even when they're fresh on the shelves, so I'm not sure how much I would trust it in the first place. Svidler's video series on c24 is excellent, I'd recommend checking that one out.

4. I played the Yurtaev for some half a year in (both on- and offline) Blitz/Rapid (never got it in my classical OTB games, as nobody played the Ruy against me in that period) and got the mainline exactly never. 
c3-d4 is decently common, but the a4-Na3 business just didn't appear on the board. Generally people either don't know it and then don't find it, or they know it but also know it invites some deep complications, so they consciously avoid it. Personally I don't go for the mainline either as White  I found 10.a5 to be more comfortable to play. Whether that still counts as 'critical stuff' I suppose is up for debate.
In general the entire system is still not very well known at "amateur" level; with most Black players I've seen still playing 6. ..Bb7 (and therefore White players largely being unprepared for 6. ..Bc5).