"I'd definitely consider paying a 'fair' price for Hi Def 24bit/96kHz - 24bit/192kHz downloads"

I wouldn't. 16/44.1k is more than enough as a consumer delivery medium. I bet you haven't got a listening environment where the noise is 96dB below the loudest music peaks you want to hear, which is what 16 bits give you.

There are good reasons for using 24bit when recording, mixing and mastering, (better still 32 bit float for processing) but once it gets to the stage where you're just going to listen to it, 16 bit PCM is fit for purpose if it's done properly.

The recording industry often uses 48k for a sampling rate, because 44.1k is a bit of a compromise on the antialiasing filters, and also because it's standard for video. Some use 96k, but opinions are divided on whether you really get anything useful for the extra disk space and processing power required.