I've had my HR21-700 for almost 3 years now. It's still ok, but it seems to be pretty sluggish lately. DTV says I can upgrade to an HR24 for $75. Is it worth it? In addition to a new/bigger hard drive and a (hopefully...) performance boost, will I gain any additional features? Is it the exact same menu/guide/DVR systems? And if I do upgrade, do I have any options when it comes to my current recordings? Or do I basically have to clean it out before the technician shows up?