As often enough, Hosts can't be merged on some Projects sometimes, e.g. after Re-Installing (HD Crash) or alike Problems, the Listings tend to grow with orphan Hosts over time.

Despite working hard to prevent it, I myself have gotten 2 spawned orphans that I cannot remove (CPDN) or merge (Projects won't let me).

I'd request to use the same principles on the Hosts Listings as the Projects do themself, display only active Hosts (at least 1 Credit in last month) and show all Hosts only on request.
Showing/Hiding could be done using BOINCstats own "Host Credits per month" figure, so it isn't a new burden on the server.

That would keep the Listings clean and display only active (real) Hosts by default

Do you want these inactive host invisible on user's hosts pages only, or also in the totals?