Yes and no. Yes, to the extent that armies are useful. Which leads to the "no", in that ground defense of planets is next to impossible, especially against superior numbers. (The best you can do is slow them down a bit so the besiegers tie up their fleet for a week or two reducing your fortifications.* And the upgraded super-soldiers (of whatever flavor) can often be dropped right into defended fortifications and still win.) Your upgraded armies will be more cost-effective than more "naked" armies, but the army isn't likely to be much of your budget, so optimizing it isn't all that useful. Still can be fun just to know you have kick-ass space marines, but you'll win games just fine without attachments.
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* That on top of the fact that taking a planet was 5 warscore, while leaving a corvette in orbit to blockade it was 7.5, so it's actually a bit counterproductive even to capture planets. Though there's an argument for taking planets just so you don't have to strand a lot of blockaders around where they're helpless against an enemy fleet. Once the main enemy fleet has been destroyed, though, I didn't see much reason for capturing a planet, making my warscore drop each time I did so.