In the good old days of film, I shot a lot of Kodachrome64... When lighting was not good your options were to use artificial lights or stop taking pictures. My second body usually had a roll of "high speed" film in it... ISO400 or ISO800..... same problem.... loose the light and you go home.
My first digital DSLR was unusable at ISO800 and topped out at a very noisy ISO1600. Now there isn't a DSLR (or mirrorless) on the market that does not produce better results at ISO12,800 than film did at ISO800.... and the numbers are slowly creeping upward.
Last night I mounted a laser pointer on the top of my camera and tried taking pictures of the cats chasing the red dot. You could not see the red dot. I turned the lights down low and cranked up the ISO to 12800 and it worked very well. These are shots that were impossible before and I have come to accept this as normal.... so yes, I need high ISO....
This is very true. Good cameras have always been expensive and out of the hands of most people. Now however, we in the digital age have gotten spoiled some with the advances in technology and I think the "noise" comparisons between film and digital are largely being forgotten.
I don't really stop and think about what ISO I need my 7D to be at to get the shot. I use whatever ISO I need to get the shot I want. I have said this in the past that I have shot as high as ISO 3200 with hummingbirds in flight and after processing the images look fantastic, both on screen and in print.
Guys are doing today with digital that could never have been accomplished with film back in the day. I think noise levels today are very acceptable even with crop sensors and you should buy the camera body that you need at the price you can afford and then use the heck out of it.
I also think because of computers too many people have become "pixel peepers" and look way too closely at the images they take. I usually print my photos at 11 x 14 and even at higher ISO's with my 7D they look great. Looking at an image zoomed in at 100% will destroy just about any image and I think any camera would have a hard time holding up to someone who is convinced that viewing them at that large of size is the only way to judge a camera's worth.
The way I look at it is, once I have processed my RAW image (regardless of what ISO I used on my 7D) and converted it to Jpeg and if the image looks good on screen, then make a print to be sure... good to go!
My 2 cents.