And that interest should be something draconian, like what payday lenders charge. If your money gets tied up for years, it ought to come back doubled.
I see this cop-baiting practice getting criminalized long before civil forfeiture.
Theirs is the money the government takes. Taxpayers (as such) are fellow victims. Voters may have supported the government's actions or opposed them—would you punish the opposition, who are on the victim's side, merely for not having sufficient numbers to prevent it?
The government claims to act on behalf of taxpayers / voters / citizens, but (once elected, if applicable) they make their own decisions about the form of that action; there is no agent/principal relationship here where the principals (citizens) would have specific knowledge of and control over the actions of their agent (the government). If people in the government choose to do something bad then those specific people need to compensate the victims; the fact that they claim, unilaterally, to be acting for someone else does not in any way deflect their personal liability for the consequences of their own choices.
Those who are most directly responsibly for the illegitimate seizures should bear the majority of the cost. That would be the individual officers who carried out the seizure, their superiors at the police department and in the state and federal government, and any judges who sign off on warrants which are later ruled invalid.