Well sure. Horses, like people, age with increasing medical liabilities. The managed anhidrosis horse may become less manageable. Any horse can break his neck and need PTS the day after the purchase price is paid.
I have a PPID horse and an anhidrosis horse. All other things being equal, I’d take the anhidrosis horse again every single time. The management is easier and cheaper. I’ll take the managed anhidrosis horse over the chronic scratches horse for same reason. Ditto front feet lameness.
I would expect any significant findings on a PPE that weren’t disclosed prior, to be an opening for price negotiations.
Is managed anhidrosis a big reduction in price? I dunno. If One AC, salt and electrolytes cost $400 per year I’m not seeing a big price reduction.