It is possible that just the stems streched and is the reason for the need to shim, but given that he had a few valves out of spec and the age of the bike, chances are it does need a valve job. A leak down test would confirm that.
But with all that said, it doesn't hurt to check the other things as well given the age of the bike and they only require some time and not much money. At worst, he'll have piece of mind that everything else is in good shape before diving into the motor.
I dont know how long he is testing either. I have seen the valves close up again after a reshim within 1 hour or ride time. The valve stems do not stretch so much as the titanium coating on the valve face wears off. When this wears off and the valve face wears, the valve sits deeper in the head causing the valve tip to sit higher in relation to the cam. The reasons have been discussed at length on this forum and others. The general consensus is that dirt and dust makes it past the air filter and that wears the titanium coating off the valve face. Once the coating is worn off, the valve face wears extremely fast. That is why once the valve clearance closes up once, it continues to close up again and again after re shimming.
All that being said, I agree completely with you on checking the other things that could cause an idle problem. I only brought up the recheck of the valves to prevent him from overlooking something that may have changed quicker than he would have though.
If his valves are still in spec, I would be checking the pilot circuit.
Another potential issue is that the bike is running like it was when he bought it now that the valve have been re shimmed and he is hyper sensitive to how it is running now. I have been an auto mechanic for 20 years and I can tell you many stories where a customer claims there car or truck is now making a noise after we worked on it that it "never made before" . A noise that is completely normal for that type of motor and I can take them out to the new car lot and show them that every one of those trucks make the same noise. Or a guy who said his air conditioning didnt work after we did a tune up and the car was never equipped with air conditioning. Another guy said he had a 6 speed manual transmission when his truck came with a 5 speed and he accused us of steeling one of his gears. I guess what I am getting at is the op bought a used bike that has valve issue. He may be seeing problems that were there already.
I dont mean any disrespect to the OP. Just human nature sometimes. I would recommend jetting it and see what it does while keeping an eye on the valve clearance.
I recommend a 150 main, 42 or 45 pilot and 55 leak. My California model came with a 65 leak but I think the other state models came with a 55. If you have to have the mixture screw out more than 2 turns with the 42 then switch it to a 45 and you should be about a turn and a half out or so. good luck.