Why don't you want mentats? They are not espionage units. There may be a bug where the list is not checking for national limits; I will investigate that.
A) National limits, though presumably you would work around that.
B) There is no gain to an instant "mentat-here-now", unlike a gain to an instant combat unit here-now. Mentat benefits are a slow trickle over time.
C) Mentats should not be available before you actually have the mentats tech, otherwise why pursue the tech?
D) Mentats are non-combat units, and so do not gain anythnig from the Homeworld trait or Elite status (extra experience).
E) Mentats aren't super-expensive, and you only get three, so you should just be building them, there's not particular reason why you'd need to spend gold to get them.
Homeworld units should be limited to actual combat units, where the extra strength from Homeworld actually matters (and similarly for the extra XP from Elite), and where its valuable to get something instantly, or where its really useful to be able to get a single unit of a type that you don't quite have the tech for.
I'd be tempted to remove transport units from the list too, they fail most of these requirements.
Its annoying when your homeworld units aren't actually useful.
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AHR94
Should siege units get the home ground +1 movement advantage?
It can be frustrating sometimes moving them around in home terrain at their slow 1 move at a time. Is there any particular reason why they don't get the bonus? It slows down AI stacks unnecessarily I think (and/or forces human player transport micromanagement).