So, I've done ski weeks at Alta for the past 10 years or so, and the majority of days there have not been fresh powder days. For those days your Bonafides should be fine.
One thing that nobody so far seems to have mentioned is that when there is a really heavy snow day, it's not uncommon for the roads to be closed, at least for a few hours, until they are plowed. Which means that unless you are actually at the mountain, you can't get up to the skiing, and by the time you do, the people already there have already skied quite a bit of it, although certainly not all. A couple other obvious suggestions - see what other people are skiing on the big powder days, and demo some skis to find out what lengths and widths work for you. As a heavier guy, wider and longer will give you more flotation, but as Philpug's video demonstrates, technique still trumps overall - a powder lesson is a great idea (especially since the instructor will know all the best places to take you, and if you get an early lesson, you get to cut the line, which means the best chance to get uncut powder). Remember that only 15-20 years ago, the Salomon Pocket Rocket at 122-90-115 was considered a powder ski, and it was significantly narrower than your Bonafides.