Heavy weather sailing
Depending on the point of sail, you are correct that a boom vang will allow you to reef at a slightly higher wind speed, but even before you have to reef, it can help reduce weather helm and heeling. This is especially true when power reeching in a range of wind angle between cracked off a beat to just below a beam reach. In that range of wind angles the boat has a tendancy to heel a lot and get unbalanced. The boom should be eased to the point that the mainsheet is no longer pulling downward at a nearly vertical angle. Without a vang you would need to have the boom in far enough that you aren''t luffing but in doing so you would have a lot of twist and the lower part of the sail would be overtrimmed. Using a vang you can remove this twist and so the sail would have a proper angle of attach up and down the sail. Without the overtrimmed lower portion of the sail the boat will be more comfortable, faster, and have less helm which at some point in the wind speed range means reefing later.
On your second question you are asking about one aspect of shifting gears. You can sail a boat so that it wants to point higher but sails slower (pinching) or you can sail lower and go faster (footing off). There are reasons to use both in specific applications but as a general rule, the fastest way up wind is neither footing nor pinching, but at a point in between. On your boat the Jib is the prime mover upwind and so if your jib is luffing even a little you are clearly pinching. You are better off easing the boom to the centerline of the boat and allowing both sails to really do their thing. In the mainsail you should have ''yarns'' at each batten tip (actually slightly above or below the batten works best) and these teletales should all be flying aft when the mainsail is trimmed correctly. In moderate to light conditions its not too bad to have the upper most batten yarn occasionally stalled and sucked into the leeward leech of the sail.
Your genoa trim is limited by the shroud attachment points and so is the limiting factor in how high you can efficiently point upwind. So to answer your question, If you are only overtrimming the mainsail for a couple boat lengths to perhaps get around an obstruction pinching probably makes sense, but if you are sailing some longer distance, trimming for a balance speed and pointing, makes better sense even if it means taking an extra tack or two.
Good luck out there.