Yeah, no. Laches is applied to issues involving various other parties with respect to damages for injuries inflicted. It doesn't apply to questions of whether a law is constitutional.
The doctrine is not nearly as narrow as you seem to believe. In fact, it isn't generally applied to damage situations at all, and is primarily concerned with the impact of an injunction.
You're probably thinking of patent cases, where it can be an affirmative defense against patent claims. However, the reason for it being an affirmative defense is not because the damages resulting from the lawsuit would have increased over time, but rather because the company ostensibly violating the patent would have become more dependent on the patent over time, which means that injunctive relief would cause more harm to that company by, for example, preventing them from manufacturing a larger number of products, thus causing a bigger impact on their ability to stay in business.
At a high level, the doctrine of laches just says that you can't pursue a legal claim if you've taken an unreasonable time to pursue the claim and that because of that, conditions changed resulting in the relief you seek being inequitable.
Other classic examples are situations where, by waiting so long, you made it infeasible for the defense to find evidence to support their position, e.g. because all of their potential witnesses have already passed away, left the company, etc. and can no longer be compelled to testify.
In this case, laches could apply because of the number of people who depend on services provided from that fund, the number of companies that depend on money from that fund to operate cell towers in rural areas, or some other conditions that have changed such that rolling back the program would cause massive harm to a large number of people and result in unreasonable harm to the government in terms of having to make good on its contractual obligations.
Basically, any situation in which your delay is unreasonable, as opposed to, for example, taking a long time because of the need to gather evidence, track down witnesses, etc., and in which your delay prejudices the defendant, potentially violates the doctrine of laches. Waiting twenty-nine years is clearly unreasonable, and clearly prejudices the defendant, because most of the people who created the program are not still around to defend it, lots of historical notes are likely lost, etc.
Hence, estoppel by laches.