How would that even work? You still need tank/laser researched to repair broken MiB tanks, and if you do, why not manfacture your own. It's not like you'll ever need more than one.
I kind of agree. Most benefits come from points and obtaining good weapons (especially laser pistols and rifles are useful at this point in the game), as well as million+ worth of sellable loot.
Of course, you can get a Tank/Laser with just 12 alloys if you repair a broken MIB tank, instead of having to put 24 alloys in to manufacture one yourself. That's essentially the marginal benefit from MIB tank remains.
If you live-capture MIB Tank Terrorist with EMP mines, you can't do anything with them except sell them for 375K base price each. In particular you cannot use the MIB Tank Terrorist chassis for your AI units directly or with any conversion (in a way you can convert alien drones to flying drones).
This might be an oversight, because it would make sense to be able to reuse an unbroken chassis the same way you can reuse a drone or a live MIB sectopod. (This is actually one of the best ways to obtain sectopods yourself early, not manufacturing one.) This might be something for SS to consider.