I suggest adding a 0.01 XCP fee on every issuance (initial and subsequents issuances alike). Also, invalid issuances should be ignored and no longer be stored in the DB.
I am against the planned 0.25 XCP fee on numeric assets.
Why fee on every issuance
From my understanding, the problem lies with the issuances table. Many use cases, like data storage, should move to broadcasts. To encourage this, a fee must be applied to every issuance, not just the first one. Otherwise you can issue an asset, pay the initial fee, but then update the asset description thousands of times for free (meaning btc fee only, no more expensive than broadcast).
Why 0.01 XCP
This is low enough not to kill legitimate usage but high enough to discourage spam. For example, a 10k collection of 1/1 NFTs will cost 100 XCP. A fair price IMO if you have a serious project but probably not worth it for the Nth punk derivative.
A cost of 0,01 XCP theoretically puts a limit of ~200 million issuances before we run out of XCP. Practically speaking, we will never run out, rather the XCP price will go up until “spamming” becomes prohibitively expensive.
This said, a static fee is not a good permanent solution. If in the future a super-majority wants to adjust the fee, and ideally make it dynamic, we should be open to this.
Named assets and subassets
Named assets should still cost 0.5 XCP for the initial issuance. The 0.01 XCP fee will apply to subsequent issuances.
Subassets should have a 0.01 XCP fee for the initial issuance, as well as for subsequent issuances.