Remember that with continuous sheets, the sheet must always be ahead of the crew for upwind sailing and behind the crew for reaching and running. Upwind, the board was definitely able to flex the trunk. Most older boats don't have any stiffening under the cap flanges. If the side of the trunk cap moves perceptibly when you push against with your foot while sitting on the side deck then you might consider bonding in stiffeners, especially if you are carrying any lead. Sails Oh, yea.
New sails are fast.
If budget is a consideration, get a new jib. It'll make the biggest difference in upwind speed and pointing ability. If your boat conforms to all the little things I've described, your potential boat speed will be as good as anyone's in most conditions.