How old is your house? Even hair dryers run more than 10 amps these days. Is it EVERY BREAKER that is 10 amp? Or maybe just the overhead lights? Mmmm, you did say that ALL of them are 10. Most strange. Do you know what amperage your power supply is? 100, 150, 200 amps? If you are not flipping breakers every time you run a hairdryer, or the microwave with the coffee pot and toaster, and if there is room in your breaker box for another circuit breaker, why not call the electrician to put in a new 20 amp breaker to run your saw and any other power tool of ordinary size?

I had an interesting variation on this situation (I've posted it here before). When my house plans were being formulated, my plumber, who was going to install the electric boiler and electric DHW, recommended 400A service. But, when the electric service was installed, only 200A was run (??, I don't know why, same GC). While the house was being built, one of the first things they did after enclosure, was to run the in-floor radiant heat (this was during the winter at temperatures as low as -20°). No problem, the workers kept warm enough, even though the window and door openings only had plywood over them. THEN, the GC realized his mistake and decided to upgrade to 400A which meant running a new line from the pole transformer to the meter (on a stand 150 feet away from the house), replacing the meter, and running a second 200A buried line to the house and installing a second load center. He said it was his mistake and would only charge me for the additional materials, but I'm not sure. My boiler can use up to 100A by itself (it's on a 120A circuit). Anyway, I still don't think the extra 200 was necessary but it's nice to have the second load center, the first one is full! Are your quotes for 200 or 300 Amps, or is that the difference?

This is how I would do it: 1) Permanently install your new 200-amp panel in the best location possible. 2) Install a 60-amp dual breaker in the new panel. 3) Run a #6-3 cable from this breaker to the old panel. Do not connect at this time. 4) Have the POCO completely remove the incoming power cable (service) from your old panel, and connect the cable you ran in step #3. (Congratulations! Your old main panel is now a sub-panel.) 5) Have the POCO connect service to your new main panel. 6) Migrate old circuits from your "sub-panel" over to your new main panel at your convenience. I'd also probably get as much of the new/re-wiring out of the way up-front as possible, just so I wouldn't have to keep having the inspector back every few months. I know that some guys will tear out a foot-high horizontal strip of wall about 18" up throughout when they do a rewire, then sheetrock it closed when they're done. This would allow you plenty of access to run new house wiring and your structured cabling, and would leave the place more livable in the mean time by not ripping off entire wall coverings. As far as why you don't want your structured wiring close to your 120v/240v wiring: Communications cable operates at a low voltage and current, and active house wiring can easily induce noise into it, thereby degrading the signal it carries. The rule of thumb, IIRC, is 12-inches of separation between a CAT-5e data cable and a power cable carrying up to 5000 Watts.

Ok, realized I didn't explain the situation perfectly clearly. The existing service coming in can handle up to 320 amps. The existing breaker box says it's a 200 amp box. So hexus is probably right, we can get up to the 320 amps by adding a subpanel. To go higher, we've got to pay the utility ~$1000 (6-something per foot) to run the new wire and hook up the new meter. I googled and found an online load calculator, so we're going to run around the house and figure out what all our appliances need, and get educated on how that all figures into what we can really load onto our existing service. Our house, with the addition, is 4300 square feet. Does 320 feel sufficient for that square footage? (2 sets of A/C and furnaces, 3 1/2 baths, double laundry hookup) And the instant hot water heater (necessitated by the fact that the bath and laundry are on the far side of the house from the existing hot water heater, and we don't want to waste all the water needed to move hot water that distance) really does require 120 amps.