Agree it's worth the $$ but only if you plan on keeping the modded amp for a long time. There's no question SMc does great work and the modded amp will sound better just ask yourself if you really are in love with it's current signature sound. IMHO it will become cleaner and more extended at both frequencies but the sonic signature should stay the same.
Upgrade McCormack or...
I have a McCormack DNA-1 Deluxe that I've been very happy with for the past two years, but I'd like to see if I can do better within a limited budget. Steve McCormack's folks at SMC will upgrade it for ~$1850 (Gold upgrade), but is there a better amp I can find for less than $3000 used (the approximate value of my amp plus upgrade cost), that might make more sense; any suggestions?