Lets be honest here - outside of a small percentage of users doing raw uncompressed video operations HDD are more than fast enough. Drives and OS both offer large caching of high use objects which reduces seek/startup time differences to a very small amount. The biggest difference is on start up and even there.. do those 5, 10, 15 secons extra really matter that much? How often are you booting? Or even resuming from hibernation if thats your thing?
As to power, idle is now around 5 or 6 watts and standby around 1. Even in a laptop the difference in power use between hdd/sdd is not going to make or break the deal. Your screen, however, another story.