We had 6 or 7 when I brought it to the whole gaming group, but I'd played it with most of them in smaller groups at least once before. It does seem like it's moving a little more quickly each time, but I struggle to picture it ever not dominating an afternoon. (Well, unless the players get absolutely rocked in the first couple Mythos phases and lose disastrously). The most time-consuming part for us is actually the upkeep phase since everyone needs to work out what they're doing before they adjust sliders and whatnot, and I don't see that every getting reduced dramatically unless we just introduce a timer that says "We have 2 minutes to do upkeep, then we move."How many players? Also, how many times have you played? It can go REALLY slow the first half-dozen or so playthroughs which can only get worse if there isn't someone at the table really comfortable with the rules.
Space Alert... Hm. I'm skeptical of the whole "audio CD-based game" genre. I guess I worry mostly about replayability, since it seems like you'd be doing the same stuff every game.
I bought Descent pre 4E thinking that it would become our standard game on D&D nights when we were down too many players. What I found is that the amount of time I needed to put into it to make it happily playable was equivalent to prepping for an actual RPG, which is what playing it left us really wanting.
The hundred dollar price tag really makes me wish that it wasn't sitting, collecting 4 years of dust on a shelf.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.