Backwards compatibility is an easy choice: Yes.
Consoles have 4-7 year life cycles at this point. By the time you hit the end-of-life, the entirety of the last gen's system fits on a rather tiny system-on-a-chip, that, at the end of the day, isn't expensive. Most of the other big expenses from the last gen, e.g. storage, you're gonna need anyway.
So why yes? Simple: Make your system an easier choice.
The PS2 was a dead-simple choice. Controllers worked, games worked, power plug worked, hell, even the video cable worked. It was a straight-up box replacement. You put your PS1 box in storage, you connect the PS2 to the exact same cables.
The Wii was the exact same way save for power/AV. Gamecube goes out, Wii goes in.
The thing is, you remove some of the choice from the matter. For the average Wii gamer, switching to the U once you've spent the money is dead-easy. Even with the Virtual Console shenanagans, there's something to be said about the peace of mind achieved from not having to turn on the old system for any reason, even nostalgia. It makes installing the new system easier.
Then comes the actual money advantages. If you do your backwards-compatibility RIGHT, you can start selling digital copies of your old games. For any company with established franchises, this is free money. Think about it. You burn through the next Zelda game and suddenly you get that nostalgia craving for the older titles. It should be ARBITRARY at that point to buy them all at your liesure.
This, I think, is Nintendo's biggest failing, and Sony's from the looks of it. They look at backwards compatibility as a revenue drain (why buy new games when I can play all the old ones?) instead of another revenue stream(why scrounge Gamestop's bargain bin when I can look through a buncha classics on the eshop/PSN? ) Heck, the first thing to die in a new console generation are a good deal of estabilished franchises that have trouble making the jump to higher requirements for graphics and gameplay that a new gen brings. Why not make it TRIVIAL for the customer base that ENJOYS the latest edition of your fantasy/sci-fi/shootin'/strategy/whocares epic to go back and see where it all started?
The thing is, consoles are closed platforms. Once a system generation is over, if production stops, any official avenues to a GENERATION of games become flaky. It's why I'm less inclined to pick up console versions of games I can find on Steam. I'm not sure, but I can imagine that consumers are becoming more aware of this. You'll note that even on Apple products, so long as you stay in the eco-system most of the dozens of apps you bought still work fine years later, and maybe even look nicer on the new device. Without backwards compatibility, a new generation is essentially starting from ZERO, and companies who don't see this are doing a diservice to both their customer base and themselves.
I could go on about this for pages but I'll cut the rant off there.