Yeah, I know, I'm a little late to the party. Played some of both of these modes over vacation (or as much vacation as one can have with a toddler). TL&DR: Invasion mode is an ultra-hard challenge that's fun. Tech race is a cool concept but winds up being an incredible grind near the end.
The Obscura start out with a massive power advantage over the scrubs (aka the other races), so you need to really haul ass and get everyone upgraded with space power multipliers. Science multipliers matter a little bit. Ion cannons too, but they're expensive and time consuming to build, and don't give you that much return on investment. All the other techs are pointless here. Half the time is spent keeping the "friendly" races off each other. Thankfully, after much trial and error, I "got gud" at fighting the Obscura. Even still, if you fight one of their assaults, you need to win it in that fight or that planet is done. Some tactical tips:
- The Obscura don't bring little dinky fighters, they only bring cap ships, so leave the anti-shrimp armaments at home. The one exception is if you're attacking an Obscura world, but you probably shouldn't be doing that yourself anyway.
- In most cases, you're better off being in front of an Obscura ship, rather than behind or to the sides.
- Only engage one of them at a time.
- Don't be afraid to run away to recharge shields or if you get swamped.
- Don't worry about allied ships getting massacred. That's their problem, not yours.
- Bring a mass driver to punch through their walls of shots while inflicting damage. Grav lances require you to get way too close, and the other weapons don't really do enough damage. 3x range + grav lance is ok though.
- The one exception to mass drivers is that triangle ship that fires the red shots that split in three. That's vulnerable to energy blaster.
Once you upgrade everyone's space military multipliers, though, they mop the floor with the obscura on their own.
Tech race mode:
This sounds like a good idea, until you realize that the last required techs are only available 90 years into the game. Ay caramba! Of course, by that point, I was at year 35 or so, so I just hit 2x fast forward while doing "expand usable land area" or "property development". In later years the amount of firepower wielded by the AI guys vastly outpaces your ship's hit points even if you have all the techs researched, so I avoided any kind of fighting at that point. I'm not terribly happy with that, as it means that the tactical game becomes unplayable in those later years. In normal play, I never have any incentive to go past maybe ten, twenty game years though.