HD video hasn't yet matured into the full pipeline from creation to presentation yet, if you don't want to spend a lot of money.
HD cameras and TVs were first, but BluRay or HD DVD burners are still pretty expensive, and so are the raw discs.
It depends on what you are doing if you want to go HD. And where you primarily watch your video.
SD camcorders can be had for a very low price now, and in one, two years you can buy a matured HD camcorder. Many say, HD camcorders are pretty mature designs already, but I don't think so. HDV is, in my opinion, and obsolete format, even though Sony just introduced new camcorders at the prosumer level. The problem is the compression of HDV, which is not field by field, but in a whole sequence, where recurring image details are only written once, but not in every frame. That saves bandwidth, but it is a problem with motion of objects, or the camera in pans. HDV is an outdated, low-end compression format.
AVCHD is much more modern, and capable. It is the same .64 codec that is used in BluRay players. There are several AVCHD camcorders, but they are working with, in my opinion, low datarates. Once AVCHD has the same datarate of 25mb/s like HDV has, then it will knock HDV silly.
With the Canon HV20 you have a very capable HD camcorder, and on that level HDV is no problem, and delivers great images. If you buy HD now, you have HD videos later, if you shoot SD now, you can't win the lost details.
But I think that resolution is overvalued. Color and the character of the image is also important. It is also a fact, that handheld HD looks far shakier than handheld SD.
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