In my experience, late March is prime ski season throughout the west. Starting mid-April, you have to consider whether the resort will still be open. But late March isn't an issue. You may be somewhat less likely to experience a powder dump, but the tradeoff is that there's bound to be decent base (even last year), and it will be warmer and the days longer.
Your best bet, honestly, is to wait and see how the season shapes up, because it's a lot easier to predict late March conditions in early or mid March than it is in mid September. If you're worried about cost, remember that the average person stops thinking about skiing after Presidents' Week, so even though there will be a bit of a bump during school vacations, it's not enough to prevent you from booking everything, from airfares to lodging, a couple of weeks out. And unless you score an early season deal now (I know Squaw is running something for another 24 or 36 hours), you will find that the deals are better if you wait. Yes, you're talking about a spring break period, but those tend to be spread out over a couple of weeks (e.g., both the week leading to Easter and the week after).