Dooku is a set piece. He is very, very helpful as a counter on attack to some of the guys you listed. But he is of minimal use against a lot of teams and usually a non-factor on defense when you can't choose who to focus. It comes down to that first turn and if you fail to stun the guy you're countering he becomes a problem on your team.
I think gearing him up is worthwhile but I don't see the importance of 7* considering the investment you have to put into him that would otherwise go towards gear or other hard shardable chars.
I replaced him with Vader (who has subsequently been replaced by Poggle) and haven't looked back. The only time I've brought him out since was against a droid team specifically to ice Poggle so the IG's wouldn't demolish me.
Also as mentioned elsewhere I'm very concerned about the guys who currently have top speed at gear 7. They may drop relative to others with gear 8 making them less capable. Dooku is probably going to be ok but it's hard to judge w/o seeing the numbers.
