1) The speaker(s) on the DVP are comparable to EVO 4G. Meaning, they're very good. I have never seen an HD7 in action, so can't make that comparison.
2) The headphones have a hissing/white noise when they're initially plugged in. I made a post on this (search hissing), and some other members confirmed that this is, in fact, the case for most phones. There are no settings that I know of for sound in general.
3) I bought insurance from SquareTrade. I think it cost me like 90 bucks. There is a $50 deductible. This is way, way better than the crap the carriers sell. I believe it covers everything you mentioned. Check their Website for details
4) Ultimately, if you have a Microsoft store near your area, call them and see if they have a device on demo. If they do, walk in and make the comparison yourself.
I am pretty happy with the device. For all the bickering that has gone on about this device, one thing's for sure... Dell will work with you (despite their long call times) to exchange the device multiple times, to ensure your happiness. It is rumored that they have an update in the works, so if you're the patient type, I'd recommend the device.