Trading Distance Stratagy

1) How often are you going to be travelling 3700km away from home?
2) How much do you care about getting Gold Medals in Useless Badges?
3) How much Stardust are you willing to waste on this?

Personally, I don't think I'll be trading ANY Mons until I'm at a Best Friends level with someone. Stardust is too precious of a commodity for me to waste on Pokémon I don't care about and a badge that (as far as I can tell) literally does nothing for me. I might do a trade or two just to see it in action personally, at most, but I won't do any intensive training until it's as cheap as possible for me.

I am 400 or so miles from home, to test I traded a 385cp parasect for a 315cp Slowbro. The Slowbro changed to 306cp. Got 550 km and 3 candy for 100 stardust. I probably will go ahead and trade some middling IV, high level Exeggutor, Vaporeon, Magmar, etc I earlier thought about throwing away but never had.

If I were in your position, here's what I'd do. You and the wife catch a lot of stuff while you're traveling. Then go home and sit on all of it. In 3 months, when you and she are bestest buddies in the game, then start trading with her, trading one of your travel ones for one of her regular, or her travel for your regular. You'll pile up distance, candy, spend minimal dust, and possibly get better pokemon out of the deal.

IMO 100 dust is already not that much for 3 candy, it's only 10-20k dust for your CD larvitars = 300-600 candies.
Even after CD 20k dust is not even close to 300 larvitar candies. 20k dust you could get in 3-4 hours without any event, but larvitar candies could take months...
Best way could be to find local trainer(s) who'll trade larvitar to larvitar. This way you'll only need 10k dust for every 300 candies.
PS: I'll not bother to collect trash from your trip if you do not care about pilot badge. One should get 3 candies from only 100km difference, it could be opposite suburbs of one city
PS2: nobody knows whether some bonuses will be added, and trade could be nerfed as well since 3 candies per trade is so awesome

100 dust for 3 valuable candy is a steal. It's 15km worth of walking for the price of catching one pokemon. I don't know how they thought this was balanced. I'm personally not waiting, will trade every chansey/ralts/beldum etc that I get from now on if they don't have super good IVs.