I have a bit of a split opinion about the mining. It does get fairly tedious after a while, but they needed to have something extra to gate those upgrades, otherwise you'd just get them naturally as you proceeded through the story and then there wouldn't be much of a reason to have them. As it is, you can do a little bit of mining and have to choose which ones you really want or do enough mining to get as many as you can. Either of these are supplemented by the boxes of material you find on missions (especially the anomaly missions that you have to explore to find).
I switched my team choices based on what I expected to find in a given mission. Miranda is very good against Geth, for instance, with Overload and also has nice squad buffs but not many mook-level organics have shields, so she's weaker there. I didn't really use Jacob until I got him Group Incendiary Ammo (being an Infiltrator, I had Disruptor and Cryo), which is really nice against organics and more so for Krogan and Vorcha because it prevents regeneration. Each of the others have their place as well.
I'm not sure what "shield improvements" you're referring to; the only shield-related ability she had was Overload.
Sindraya, Assassin
<Ravensflyte>
"Oh, hell no," Kylar said. "You cannot fly. Tell me you can't fly."
[Sindrak (DoK), Wingus (Choppa)] | [Drakhon (Thane)]