The titanium Apple Card looks slick (with the sound to match), but you may need to treat it gingerly if you expect it to look as pristine as the day you got it. Apple has posted a cleaning guide for the physical credit card that warns against storing it against leather and denim, lest they cause discoloration that "will not wash off." Yes, that's right -- you could end up with a nasty-looking card simply by putting it in your usual wallet or pants pocket. Many leather wallets have linings, and plastic cards have their own issues, but this suggests it's more delicate than some would like.
Accordingly, the same guide advises against putting it in direct contact with other credit cards or loose items lest you scratch that pristine titanium surface. And if there's a stain you can clean off, you'll want to wipe it down using a microfiber cloth moistened with isopropyl alcohol.
This isn't functional issue on the level of Antennagate. It's not like your card will stop working just because it's a bit dirty, and you'll have an incentive to use Apple Pay more often regardless. With that said, the titanium card is as much about flaunting your status as it is making purchases. It's hard to do that when your card looks like it went through hell, isn't it?