Thoughts on Usher S-520's...upgrade?

Hello all.

First let me say that I'm fairly new to the hi-fi world (about 5 years now) and have so far centered on "budget hi-fi".

I love monitors (and they fit in my office where I do most of my listening) so a few years ago I did my research and bought some Usher 520's (before the price hike) based off the glowing reviews (professional and user). I added an Outlaw LFM-1 Compact to fill out the low end (I'm not a huge bass head; the Outlaw's volume is halfway and the crossover is right at 60 where the Ushers start to drop off) and it integrates well I feel with the 520's.

Well I've loved this combo for years now (I am running it off of a Cambridge azur 640a v2 amp and DAC Magic with lossless files from my computer) and have left it alone since it is certainly "good enough", if not great sounding to me.

But...sooner or later upgradeitus hits us all right? Or, if not that, just curiosity at what other monitors might sound like and if I'd prefer them over my 520's, since, after all, these are the only "real" pair of speakers I've ever owned.

So my question is what the general consensus is of the Usher S 520's here, especially compared to more expensive speakers. Is it worth it to go up to $500 to $700 ish (new msrp anyway) monitors? Will it be enough of a step up in SQ to justify the cost (remember I got the 520's for $330 shipped)? Or do the Usher's lack in some criteria that I can't really hear since I've never compared them to other good monitors in their price range or higher? I will say that I love their neutrality and transparency, detail and accuracy (I don't like "warm" or "natural" sound), but it seems that they are a little lifeless or flat as well, maybe even a little recessed in the mids (voices can be a little distant it seems).

So, short version, is there something in the next tier of monitors that will have much of the Usher 520 SS (accuracy, transparency, revealing, detail, neutrality, tight/taut bass, etc.) while adding maybe some excitement or energy? Perhaps also go lower in the bass region so I can listen to them without a sub without them sounding as lean as the 520's do without my sub. I'd like an all-rounder since I listen to much of everything, although I mostly listen to rock (all decades and genres), synth pop, and singer/songwriter. I also would need speakers that sound good a lower volumes (I mostly listen at mid volumes) although can crank too (the 520's seem to do this).

Thanks for any input, so far I've got a list of about 20 monitors to look at, but that's fun to do and I take a long time looking and considering before I buy anything!