For what it's worth, I have a high ANA (ranging between 1:320 - 1:640, homogenous pattern, over at least a decade), with a bunch of systemic symptoms, but no other positive inflammatory/autoimmune tests and no other autoimmune diagnoses. My rheumatologist (a lupus specialist) thinks the ANA might be related to the diabetes somehow, although I feel like I'm always waiting for another autoimmune shoe to drop. I do however seem to have a genetic connective tissue disorder (likely hypermobile Ehlers Danlos Syndrome), which accounts for a lot of the symptoms we thought might be lupus and is linked to some autoimmune diseases (not necessarily T1 diabetes thought) and mast cell dysfunction, so I'm not sure if my autoimmune weirdness might actually be a feature of that.
Anyway, I agree re: checking for a broader range of inflammatory arthritis—my close friend has psoriatic arthritis as well as celiac (more evidence of these things clustering). It took a while to diagnose, because it's not as commonly looked for as RA. She now takes embrel, which helps somewhat.