Is there any reason to get the +2 to grenade count for rank 5 of a grenade for any squad member?
2 Answers
Yes, Squad mates have limited grenades, which is why they don't use grenades on their own. Note that if you don't manually use your squadmate's grenades, there's still no reason to upgrade, as they're not using them automatically.
Squadmates gain grenades when Shepard does, so it makes sense to keep squadmate's grenade count at Shep's level. Assuming you use the squad's grenades.
Yes, grenades are the explosives you want without the weight of a rocket launcher, they may not be as good, but they are affective, so as they say... the more the merrier :D