For the time being standard definition is pretty much all you can sell to scuba diving tourists, and shooting it in HDV and downconverting it is more complicated than shooting it direct in DV. So you have to make a judgement about how long you feel the SD market is going to last, and whether you're interested in HD stock footage or not.
Typical scenario I'm getting recently on the boat:
Customer: "Can't wait to see me with the manta ray back home in high definition on my new 42" LCD HDTV!" 
Me: "Actually it won't be in high definition. But it will be widescreen and it will look great."
Customer: "But you're using an HDV camera." 
Me: "Yes but I'm converting everything to standard definition because you've got no way to play high definition material yet."
Customer: "But I've got a shiny new 42" LCD HDTV" 
Me: "Yes but your DVD player only plays standard definition DVDs. Unless you're telling me you're one of the first purchasers of a Bluray or HD-DVD player." (psst... he might have a player that can play HD DivX or WMV but let's not commit ourselves to 2 days' extra work while the rest of the boat gets SD)
Customer: "But... but...." 
Me: "And even if you have one of those, I can't make you a Bluray or HD-DVD disc because affordable authoring software, media and burners have not arrived yet. I can't even author Bluray in Sony's own authoring software."
Customer: "So when will you start offering those?"
Me: "I guess some real demand will pick up in a year or so. Then I'll be charging a premium for the HD version as long as most customers are still ordering SD."
Customer: "So I can email you in 3 years' time and get a copy of this in high definition"
Me: "The best parts of it, yes. Sadly not the whole video as I don't have enough storage space for that"
Customer: "So why did you buy the HDV camera?"
Me: "Stock footage and hopefully the occasional commission for TV"