Is there anything to stop me renting two cars at the same time (one for me and one for my wife) - both booking in my name / wizard with second driver (my wife!)...

Much cheaper this way and we get Avis Preferred...

I'm worried they will think duplicate booking and cancel one of them?

Thanks

Nah. I've done this many times. I think the most I've had at once is 4: personal one for home (my car was totaled so I had a rental for a month) and a few work cities. For work, I always rebt the car since I'm Chairman. I often leave town and leave the car w a coworker and get another for myself on the new town. Keep repeating and no issues. A few years ago, they would ask "do you have another car out" and just have you verify your info. I haven't had them ask in a few years though.

What about two identical bookings - same time pick-up etc...

I don't think it would be a problem. Avis lets a "life partner" (same address on DL) drive your car, so you'd have to show both DL to prove you meet that criteria. However, why not just book 1 in her name and 1 in your name? You should be able to get the same price with/without your name (just use the same AWD/coupon). When you get there, you can always ask for upgrades if they don't automatically give them.

That depends on the airport! How are you both going to drive out of the airport if it's one of those where you pick up the car and then the only place they check your drivers license is at the exit? By then, don't each of you have to be in your own cars? Is the second driver allowed to take the car out of the lot (at any airport where a Preferred car is checked against the driver only at exit), or only allowed to drive it later (after leaving the lot)???

I don't see how that's cheaper than your wife signing up for Preferred herself and then using the same AWD you do. You should then both get the same rate. (Of course, on her first Preferred rental ever, I believe she'll have to visit the desk and show the linked card.)

Now, if you know for sure this is a location without a Preferred board (ie, a small location where you both have to visit the desk to get your keys and show your licenses, that may be easier. But then there's not as much Preferred benefits, is there?