In my experience, Bangkok is not the most wife-friendly city in SE Asia, especially if one is on a budget. That is not to say that the whole city is the den of sin and iniquity that popular media tries to make it out to be (oh man, I really didn't like that installment of The Hangover . . . so white-man ridiculous).

I was there in 2010 when the last political thingy was going on and honestly, I didn't even come into contact with that stuff while I was there. Anyway, a cool time to go might be for Songkran. Bangkok is ok for a few days, but it's not much on scenery.

If you plan on ending up in Vietnam, you might as well go through Cambodia, especially since Siem Riep and Ankor Watt are fairly close to the Thai border. From there, you could hit Phnom Penh and then up to Kratie to see those pink river dolphins, if they're still around.

From Phnom Penh to Ho Chi Minh City, Vietnam, bus is the cheapest and it takes about 8 hours or so. Just make sure not to bring Baht to Cambodia, since the exchange rate is really shit for anything except dollars, pounds or euros.

Pham Ngu Lao street is where most of the backpackers stay in HCMC. District 1 is where most of the fun stuff is.

SE Asia is good for jungle stuff and beach stuff on the wife-friendly and gentle travel side of things. You can get real gritty if you want though, very easily. Especially in Cambodia. Rent a dirt bike and start riding. In Northern Vietnam there are motorcycle tours through the mountains. These tours use these shitty old Minsk motorcycles that somehow do pretty well in that environment.

A good wife friendly thing about SE Asia is that legitimate massages and spas are very, very cheap. In fact, I used to go to a place to get a sauna, a face massage and a full-body massage, which took about 3 hours all-told, for just about 30 bucks. Just say you want to take her on a spa holiday or something.