"Worth watching" implies that watching is expensive. It's really not. A full-body MRI scan is about $1k, and it can be even cheaper.
So if you have abnormal findings in 10% of patients that merit follow-up scans, you can trivially do a series of 3-4 scans without affecting the overall cost too much.
Doctors simply need to get out of the headspace where MRIs are extremely scarce tools of last resort and treat them like we treat blood tests.
I totally agree. US healthcare is broken and costs aren't tied to the reality of how expensive something actually is. I have very high hopes that modern medicine is in for a massive disruptive change where things like full body MRI, along with analysis, could be done very cheap and with no admin overhead. In that model 'we see something we aren't sure of. It is probably nothing but to be sure we want to do follow-ups' is far less of a problem.
A lot of this however is how it is discussed with the patient. Discussions about the likelihood of there being a real issue when something is seen need to be clear and informative without being alarming. 'We did a routine scan and these often show transient artifacts that turn out to be nothing, but in an abundance of caution we want to do a followup' is totally different than 'we saw something we are concerned about and need to do a followup'. How things are messaged really matters.
I think you're missing the point. The psychological cost of a conditional-positive result is nonzero, and can be very significant (I speak from a little bit of experience here). But far more importantly: the physiological cost of invasive followups when you eventually trip the threshold of "time to go explore with a scalpel" is very high, and the missing evidence this story is about is whether you can get to that threshold with an MRI.
Treating MRIs the way we treat blood tests would almost certainly result in huge numbers of needless invasive procedures.