Best option for Amp upgrade...

I have a McCormack DNA 500 that I like.  I'm considering spending about $4k to have it modded by Steve McCormack (SMC).  Alternatively, I could sell the DNA 500 for about $3k and have $7k to spend on a used (or new) solid state amp.  I'm inviting opinions on which would give me the best bang for the buck.  I'm hoping to achieve greater resolution and detail.  Bass control is not an issue!  Here is the rest of my system:

Pre-amp - CJ ET3-SE
Speakers - Rockport Mira II with REL G2 sub
Source - Aurender A10
Cabling - Transparent Ultra MM2 speaker, Gen 5 Super interconnects, Reference power cords (mostly) 

If you suggest a new amp, I'd be interested in your recommendations.  Thanks!

The DNA500 is already a pretty hi-rez and detailed amp even in stock form.  I think what you may be hearing, despite its many other considerable strengths, are some limitations of your preamp -- at least that's what reading reviews of your pre lead me to believe.  Have you considered tube rolling?  I'm not familiar with your interconnects, but that's another area maybe worth exploring to tweak the sound of your system a bit.  Just throwing some other thoughts out there FWIW.  Best of luck. 

Sell it, and move on. 

Hmmm, thoughts. What about Class D? NuForce and Bel Canto, among others, get excellent reviews. 

Tubes, used CJ Premier 11 or 8. 

Ayre is also something you should consider. 
Unless you have an emotional attachment to the amp,move on.At some point you will want a change and those mods will be worth about 10 cents on the dollar.If solid state is your preference you may want to consider a Bryston 4B3 a clearly more evolved design than earlier models with a higher than average resale.Addiction,the gift that keeps on giving.
With amplifiers, new is not always better, particularly when comparing to Class D.  I would be curious about how many of the folks saying "sell" have owned McCormack gear, and particularly how many have owned his amplifiers with full SMc upgrades. 

I have a DNA-2 LAE  with SMc Signature upgrades and it sounds great.  I chose to keep that amplifier over a pair of Ncore, NC1200 monos.  I also own a pair of high-powered conventional Class A monoblocks that are in my main system.  I like the Class A amps better than the McCormack/SMc amp but both sound good. I believe there is a picture of the DNA-2 on my system page and the work quality is exceptional.   You would be hard-pressed to find that quality in an amplifier today under for $10K or even much more.  BTW, more than most other manufacturers, Steve has a history on his gear and he is very aware of which parts are at risk of degrading or wearing out and he will address any of those issues during the upgrade.  If you like the sound of the amp now, the upgrades will improve on that.  The sound will still be similar (i.e., it will not be a totally different sounding amp) but it will be more refined,  with improvements in tone, treble smoothness, and maybe dimensionality, among others.  BTW, I have also owned the DNA-500 and it is a very nice amplifier.
while I agree that usually degraded older caps/parts and modded products not holding value are often important issues, I don't think these apply to SMc upgraded products...