If he insists on buying new, trade in that PS3. You really don't need both, promise. I'm fairly certain the 4 can handle all the 3 games and do all your streaming. As for a 'back up' device, get a cheap HDMI cable and connect your lap top to the tv if something happens. There are only two reasons I can think of streaming would stop working on the 4 - something's wrong with the internet (in which case, you're shit out of luck until that's fixed) or something's wrong with Sony (where your 3 would be just as useless as your 4). Your Wii can also stream Netflix and such, but if you're hardly using it, you might as well trade that in as well. I think I just read GameStop was offering a pretty good deal on trading in 3's for 4's. Obviously, used/refurbished is still better money-wise.
Double check my facts, but I'm pretty sure I"m right. Then again, I'm more of an XBOX girl myself.