I don't ever remember getting in a car and thinking "ooh I wish that steering wheel was warmer!!.......well not since driving classics with Bakerlite ( and they were far worse for burning you in the summer!!)!!
To me it ranks along side heated seats....pointless as when they need to be warm is when you first sit on them as that is the only time you might notice they are cold (unless you often wear a mini skirt....something I hardly ever do now!!!)....but they wont be warm when you get in unless you have remote start. I guess they might have a place on a convertible though.
As far as petrol and derv is concerned....well as much as I've enjoyed the high torque flexible power of my car and racked up 171,000 miles on it....would I buy another?.....nope. Life for non E6 dervs is going to get very tough (as said above this is already being reflected in their prices on the use market) and its only going to get worse.....and if I was given a E6 one?....Id sell it....they are just a big bill waiting to happen.....the last thing you want when one of the main reasons for having a derv in the first place is economy. Next car will be petrol and Ill just have to suck up the extra fuel costs.....don't do as many miles these days anyway.