However, I was more interested in hearing if "the value" was comparable to Starcraft, which from what I've read, is one of the most replayable games ever made. When you spend ~$50 on a game, you'd like to know if it's a good investment.
You can't really measure the longevity of a game like Starcraft to, really, anything. Understand, Starcraft is effectively the
sport of choice for an entire
nation (South Korea). That is, people actually go to studios to watch and cheer Starcraft players. They talk about Starcraft matches like Americans do Football games. They know terminology like "micro", "macro", "rushes", etc. Professional Starcraft players fund their professional play through endorsement deals, and they live quite well off of them. And nobody there finds this at all odd.
Sins of a Solar Empire probably won't be that. Starcraft II may not be that.
Starcraft is one of those unique situations, where it was the right game in the right place at the right time to captivate millions for 10 years now. Assuming Sins has equivalent depth (obviously in different ways, due to being so very different of a game), it probably won't last as long, simply due to not being the right place or time.
They might be worth one or two replays. Not the best value out there.
The longterm value of most FPS games (those that have longterm value) is in the multiplayer component. As is the value of Starcraft. People don't play Starcraft for its singleplayer.
Of course, value is in the eye of the beholder. I've played GalCiv2 in terms of number of hours far more than I have Half-Life 2, but I wouldn't say that I
value GC2 more than HL2. They're both money well spent, but well spent for entirely different purposes.