I have one dedicated 20 amp circuit/line for my amp and two dedicated 15 amp circuits/lines for my digital source and preamp.
I believe that so long as you have decent to excellent quality equipment, you should realize a significant improvement at both the micro- and macro-dynamic levels.
Therefore, assuming your equipment is decent quality or better, you should consider the dedicated line(s) no matter what you decide about upgrades.
And as far as audio upgrades and tweaks, the dedicated lines are among the cheapest tweak.
I would not recommend a sub-panel. Have your electrician replace the standard circuit breaker with a double circuit breaker.
You may also consider purchasing a roll of 10 gauge 99.95% OFC romex from perhaps partsexpress.com at $100. It's better than the Home Depot standard romex variety.
While you're at it, you could also install some hospital or audio grade wall outlets. Even the cheap 20 amp wall outlets at Home Depot are usually significantly better than the even cheaper 15 amp outlets just in the way they grasp the plug.
-IMO