I would hope/expect that someone who could afford to buy a horse could afford to replace everyday necessities if they were falling apart. The OP asked about splurge gifts. Of course you could give a practical gift of everyday stuff instead… But that’s not what the OP asked about
Saddle pad with farm name/logo!
If you want to go a little bigger, mountain horse has an AWESOME jumper coat I just bought for only $110! Seriously gorgeous and so affordable.
HandsOn Grooming Gloves.
A nice fly switch.
If you’re friendly enough with the person that it won’t go the wrong way, some of those sports body wipes.
Pommel or cantle bag to fit their saddle.
(These are all on my “I should ask for these things for holidays” list…)
I would go with a gift card to somewhere like Dover or Smartpak. Always great to get a gift card where I can go shopping without taking the hit on my own bank account. And I usually tend to buy things I would never let myself splurge on.