There is sound absorption drywall you know. It's roughly 8x quieter than regular sheet rock. Here's a product called "
QuietRock." You can thank me later.
quietrock is a marketing gimmick. It does very little for the cost. for the same price you can do alot better.
You can do what I did to my apartment and layer all the walls and ceilings in that room with QuietRock. It is pretty simple. Just use drywall glue to put it over the top or your current walls and ceiling. Then use compound to tape the seems and screw holes. Sand it down and paint. You now have a quiet room.
http://www.quietsolution.com/html/quietrock.html
what's helping here is that it's another layer of sheetrock, not the fact that it's quietrock. Also certain glues work better than others for soundproofing, and you have to be careful applying it. Doing something similar is probably op's most practical improvement, unless he's willing to tear out the existing sheetrock and hang genie clips / hat channel.
There are a several things you can do to minimize noise. The biggest thing is to replace your sheet rock walls with quiet rock and replace your insulation with denser insulation made to absorb sound. This makes a huge difference. You also need to insulate around all the electric outlets, switches, HVAC vents and door frames. There are special products for this, check out Home Depot. It doesnt matter if you have carpet, tile or wood floors you need a decent pad underneath the thicker the pad the better the sound absorption.
The "soundproofing" products for outlets, etc, are also overpriced gimmicks. standard firestop pads work just as well and are cheaper. block the air movement, block the sound. It's not rocket science.
I haven't read the whole thread, but aren't you perfectly in the clear as long as you're not making noise too early in the morning or too late at night?
different areas have different noise ordinances. Some are definitive about the nighttime thing, most aren't. Mostly it's left up to the judgment of a responding officer to determine whether something is causing a disturbance.
Here's really the big thing: most modern townhomes/condos are designed to code minimum, if that. Plans examiners generally don't look at sound transmission properties, so wrong designs will usually get through, and on top of that, even if designed to code, it rarely gets built that way. In practice you can generally take the STC of a designed wall and subtract 5-10 DB (A weighted)
...until someone gets sued. It's the #1 lawsuit issue for developers, architects, and contracts who do multifamily construction, primarily because it's sort of a subjective thing, and because it seems to be std. practice to not follow building codes (or best practices) when it comes to sound. Realtors and marketing people like to talk up sound privacy to potential buyers, and almost always wind up making unrealistic promises, given the above.
That's not to say that you can't do quiet shared walls. It's flat wrong to say you can't. It's fairly easy for a small to moderate cost increase, but it requires knowledgeable designers and good contractors (with lots of double checking). A double wall is generally the practical best (with thick gyp-crete on the floors), but in practice most people are happy with genie clips on at least one side of the walls, using firestop products on switches/outlets, and a moderate gyp-crete thickness on the floor. Pretty easy and works very well.