Ignoring all other factors (games, Natal, Arc, etc.) a 360 price cut would boost sales of hardware but the people waiting for the price cut to buy a 360 will have very little return on software sales(opting to buy reduced priced games or used games) and a very low percentage would be paying for Live's subscription. The reason for that is obviously that if money was the sole factor in not buying a 360 then that consumer probably doesn't have a lot of money to buy games, accessories, live, etc. Also the 360 has already had an entry price point of $200, so even if it wasn't the most desirable SKU, you would have to assume that the arcade eroded a lot of the impact on a sales boost that cutting the price of other 360 SKU's to $200 would have.
The 360 is already passed the point of acceptance as well so even if the price cut increases the user base it will hardly impact the mainstream/casual appeal of the console. The only place it might work is in Japan but I still doubt that as the country seems to be set in it's ways, at least for this generation.