People want Tempest replaced and White Cap quad is underutilized.
I would look to consolidate, not replace 1 for 1. How about replacing White Cap and Tempest quads with a HSQ top to bottom up White Heat? The alignment is perfect. The only thing you would need to do is find a way to get beginners off the summit down to where the top of the Tempest chair is now to pick up Over Easy (Green route down). Maybe this could be achieved by hooking something more towards to back or even the front with less grade across the fall line?
After that I would say replace Spruce. I think Locke should be last, it has been reliable and there are only two routes down with snowmaking vs 4 on Spruce. You also can ski 75% of Locke from Barker.
I had the same thought on just replacing the two lifts with 1 ttb hsq. Like you said though there would need to be a better way for low intermediates to exit the whitecap summit.