Mike, welcome. As to when the relationship between price and features "stops being linear", the answer is that such a relationship never even starts. In audio equipment, as in many other things that are sold to us, we have to pay a lot more for relatively small(if any)improvements. So, don't worry about finding a financial "sweet spot"; get the features that you want at the lowest price possible. From your description, you do want significantly more than a basic feature set, and receivers such as the Denon 3808 and Onkyo 876, which can be had for around $1000, are prime candidates.
As to power, anything in the area of 100 watts should be more than sufficient for the vast majority of setups. There's no such concept in reality as "real watts". The law requires that amplifier power ratings be in fact true. A 100 watt rating is actually what has to be delivered per channel(dividing 100 by the number of channels isn't a meaningful exercise)with at least two channels being driven simultaneously at full power for at least five continuous minutes. Unless specifically stated, this doesn't mean with all the channels being driven simultaneously at the full rated power, but that's a lab test number which has no relation to real-world home use.
"Upscaling" relates to the requirement that all the "pixels"(picture elements)in a TV screen be filled to present a full picture for viewing. When a standard definition TV transmission or standard DVD content with 480 pixels per line is sent to a TV display which has a "native resolution" of 720 or 1080 the missing pixels have to added in to show a complete picture, and this is done by mathematically calculating extra pixels to be added. The result is that the picture is fully displayed, but not with the resolution that comes from a source that provides a "real"(here that term does apply)720 or 1080 output. The upscaling can take place in a player or receiver or if not done previously, in the TV display itself. Which of these does the best job of upscaling varies between the various units.
An HDMI connection can carry both audio and video and the video quality may be(but isn't necessarily)slightly better than that carried by a component cable video connection(which requires a separate audio cable connection).
