Active gathering of resources is an important part of the SC2 experience. It was satisfying to finally find one of those molten planets filled with awesome metals, but also full of lava, lightning, and earthquakes. Then having to decide if it was worth the risk, etc., etc.
It was also a very repetitive and time consuming process that had no business taking up that much playtime. Seriously, it might have been the way I played, but it seemed like you couldn't do much of anything until you mined out a system or two and got some toys put on the precursor ship. It was fun to a point, but when I went back in another playthrough, I wanted to get to the rest of the exploration and story part a bit sooner.
So, for me, the question is not whether it should be included, but just how it should be implemented. A few ideas:
-Risk/Reward - This shouldn't necessarily be a sliding scale, but there should be a general correlation. You want big deposits, it's going to be risky, even with a decked out lander. Having the occasion "pot of gold" planet with easy access to tons of resources should happen every once in a while too, but will be rare.
-Mining competition - The same gathering mechanic doesn't have to exist for every single planet. Maybe there is a gathering operation already in progress and you can trade for materials or maybe...away party with phasers and take it by force? Races with other aliens as you both try to grab limited resources might be fun, etc.
-Less hauling time - Lugging back a full ship is just not that fun. The goal of continuous exploration should be more important than trips to and from one central sale location. Perhaps have lots of ore processing outposts through the galaxy that will buy your stuff. They could have different prices for different metals just to spice things up. Maybe have a hauler upgrade for the main ship. When the cargo is full, it heads off to sell the ore for you leaving you with little, if any, remaining cargo space, but doesn't require you travelling back all the way to...wherever.
-More "Stuff" to do - Collecting biomass and collecting minerals was pretty much the end of the list in SC2. How about more things when you interact with planets. No reason not to make planet encounters more like Star Trek. More types of planetary interaction could add a new dimension to the exploration aspect.