I've bought for EUIV, and I can't say I regret it - most of the substantial gameplay changes are available in the free patch, but the additional features of the expansion itself are all worthwhile.

This expansion pack truly does add a lot to the game in my personal opinion. Finding an archeology dig on a planet becomes a source of excitement not just for the rewards but for the story behind the dig. If you're not one for lore or story I wouldn't recommend the pack, but if you're into lore I couldn't recommend it more!