If someone were to do a longer rest at beta temps (like 60-90 min) then mash at alpha temps for like 30-40, it seems like you would get the best of both worlds right?
You just hit on the reason some brewers (especially lager brewers) like to step mash a beer - to have the best of both temp ranges. Alpha works best at 154-162°F, while beta works best between 131-150°F. So if I mash a helles for 45 minutes at 145F and 45 minutes at 160F, I've created a beer that will both attenuate well with a nice drinkability (from the beta rest), and also have some nice body and foam stability (from the alpha rest).
Jury's still out if you ask me. More experiments are needed. Personally I'd rather save the time and extra dorking around for something that we most likely can't probably taste the difference anyway, just split the difference, mash in the 150s for 45 or 90 minutes as you prefer, and call it good.
Another thing I wonder about.... if beta amylase doesn't all die right away at 154 F or so, doesn't it make more sense to do a reverse "step" mash (actually more of a "smooth" mash) starting at that point, not insulating, and allowing the temperature to fall to the mid 140s by the end of the mash? Anyway, that's what I do almost all the time, without thinking too hard about it and without worrying, and with very good results IMHO. Way less effort for probably very similar results.
But, you know, many people just can't help but play with their food. Insulated mash tuns.... bah... humbug.
I agree that the jury's out, too. I've been experimenting with step mashing (again) for about a year now. The one difference I'm absolutely convinced of is the benefit of better foam from the alpha rest @ 160-162F. It's an easily noticeable difference IMO. Flavor wise, I don't find a single infused lager to be inferior in any way (if mashed right).