If no hidden infection is found, and getting the cysts better doesn't have an impact on her numbers, she said she would start with testing for pancreatitis (seems unlikely as Chewie has a solid appetite and no GI signs whatsoever, but you never know I guess with cats) and doing full body X-rays to look for cancer. Only then, if those were negative, would she test for IAA and acromegaly, since she feels the ratio of benefit provided by treatment and financial/medical burden of that treatment for the cat and owner isn't very favorable.
Depends how much you like spending money on tests that tell you nothing. Cancer isn't going to cause her to need higher doses of insulin, so I think those x-rays are a waste of time and your money, unless the vet is thinking of them in regards to the cysts. There is a reason that we suggest that people get their cats tested for acromegaly and IAA when their cat gets to 6 units of insulin, if they are on an all low carb wet/raw food diet. We have seen cats get close to six units with other conditions (eg. pancreatitis, heart disease, hyperthyroidism, infection), but not over 6 units. Some people with cats on higher doses don't get tests done. The only problem with that approach is that knowledge gives you power. If acromegaly, there are treatments that help. Especially cabergoline which is a fairly cheap daily medication that can greatly improve quality of life. Plus we've had a handful of cats go OTJ on it. I had a cat with both acro and IAA, and I don't regret for one minute the SRT (radiation) treatment we did, which was the only option at the time. There are more options now, so I might have chosen a different treatment, but it did give her several years of much better quality of life. I consider that a huge benefit. There wasn't a huge medical burden until the last part of a year when the multiple diagnoses made things more complicated.
Just so you know, it's not uncommon for vets to be reluctant to run the tests. Many vets "of a certain age", were taught that these conditions were very rare, but newer studies have show around 1 in 4 diabetic cats have acromegaly. I had to ask my vet to humour me, several times, in order to get the tests done. And tell her exactly how to get the tests done. She was very surprised by the results of the "exotic tests", but willing to work with me after that to learn what to do.
To set Chewie's dose in context with travel, Neko rode 3 days to Fort Collins on an 8.5 units dose. She saw less insulin resistance on the trip, not more. I lowered her dose for the trip back. We had one kitty who rode even longer on a car ride to Spokane WA from the east, with an 49 unit dose reduced to 45 units for the trip. No, that was not a typo. That cat was much more resistant than Chewie. Pig didn't see his first blue until 59 units. There are several additional examples of cats I could find, that travelled when their doses at the time were higher than Chewie's. A cat needs whatever dose they need.