Is the iodine test for starch conversion pointless?

Its probably a good idea to do the test when you first go to all-grain using malted barley but once you are dialed it might be optional. HOWEVER, certain malted gluten free grains, such as millet and buckwheat for example, do not readily self convert. You can either do complex step mashes to achieve this, or do a simpler single infusion mash and add enzymes (alpha amylase) and in this case yes you want to know definitely if the conversion did indeed occur. So, no its not pointless either way you look at it but it might be optional if your experience makes it so.

Seems strange to me that so many people are prepared to trust their own "untested" experience to know when a mash has got complete conversion. Kind of like an electrician saying I've never tested if circuits are live before working on them so testing is a waste of time.

I mean don't get me wrong, it is not the end of the the world if your mash did not achieve full conversion, but even with the freshest of malts and the right temps, I have still had the test fail now and again, an extra 10 - 15 minutes in the tun has sorted it out. BUT and here is the nub of it. If I had not bothered testing I would have just assumed that in my experience my mashes always completed on time every time.

When you consider how much time, effort and expense we put into a batch of beer, is the 20 seconds and a couple of pennies it would cost for the test that big of a deal that it is worth skipping?

If you have been regularly brewing using the same ingredients and same gear for years and never had a failed conversion test, then I can understand not bothering with the test every time, but in all honesty untested experience where you just assume something has been right all along, is not worth anything.

IMO, yes it's pointless. First, it's pretty much impossible to not get conversion given a sound recipe and hitting your mash temps. Second, as you've noticed, it's more than possible to get a false reading. I haven't done an iodine test in the last 13 years and haven't felt like I needed to do one.