1. F4i Valve Check interval is at 24K, so if you are at 36K - you are well overdue. So the 'shop' you are going to is giving you bad info.
2. "but my shop says if it runs fine don't do a valve adjustment till 60,000km " --> If you wait, you might have way bigger issues by then. Might result to a bigger bill

... again the 'shop' you are going to is giving you bad info.
3. Valve out of adjust will take a long time to give you issues, if they are too tight - it will cause starting issues. Too loose - you don't really want to think about that one...
4. if you aren't getting your valves checked at correct intervals - what other maintenance are you skipping out on ?
4. A 2004 R6 is a very desirable chassis / platform, it is still one of the premier handling chassis out there. And for people who've been around - they love that little R6. It is also eligible for the 'lost era' class - so it makes it even more valuable of a bike.
5. "almost outta life even though" I take care of quite a few forum members bikes, been taking care of them since they were almost new. Some of them are well ever 60-80k + now. And those owners will run circles around other bikes in their class and track them, tour with them etc. So they are hardly out of life. I personally have a 03/04 zx6r. Had 3k when i bought it - rode that bike for 2 seasons. and now she has 65K - ran like a top. Ex-GF had a 05/06 636 - sold that bike at 50K - the owner prob is still loving that bike.
I would not think twice about buying any of those bikes. They will run like tops. But i've seen plenty of bikes under 20K that are iffy to say to least.
6. "CHECK MY YOUTUBE CHANNEL MOTOVLOGGING THIS YEAR" <<--- Are you here to ask a question or self promote ?
One of the biggest issues is previous owners not maintain their bikes and abusing them....here is a video from your 'VLOG" that is a good example of what you don't need to do. Burns out are hard on drive system and clutches, not to mention the motor. Wheelies are hard on head bearings and fork seals.
[video]https://youtu.be/jgaXs7b5-z0[/video]