One of my light air problems is completely toasted sails... I believe they are original 1977, and generate all the lift of tissue paper. Budget constrains me to a new main this winter, and a new genoa next year. This stuff was tolerable before I started casually racing and realized how far off the performance benchmark my boat really is.
Having said that, for not being a upwind sail it sure holds its shape better than my dacron 150% does in extreme light air, and all that extra surface area seemed to help. It brought my boat from .25kts up to 1-2 kts when nothing else seemed to work.
Perhaps, but what kind of vmg were you making? While it is true that the golden rule of light air sailing is to get the boat moving, it doesn't do you any good if you can't dial up to a decent point once you do get moving. What you need for ultra light air is a "drifter", which is a very light headsail or staysail. size is not as important as light weight. Often they are not even overlapping sails, but they have the ability to give you a foil shape in the lightest zephyrs. You could probably find one used pretty cheap if you look.
It is definitely challenging sailing in light air with baggy all purpose dacron sails, but it can be done. If you talk to the loft that is going to build your new main, they may be able to give your headsail a little "nip 'n' tuck" that would help. You could also get some light weight sheets so you aren't weighing the clew down so much. Lots of leeward heel will help the sail hang with some shape, and one of the crew on the leeward side can hold up the clew so the leech doesn't choke off from it's weight. If you can get gravity to put some shape in your sail, even the lightest wind will start to generate lift and before you know it, you are leaving a wake. It takes a very gentle touch on the helm and sail trim, and minimal movement on the boat.
The thing is, when you do get the boat moving, and the breeze fills in enough to fill the sails on it's own you will be able to smoothly dial the boat up to a decent upwind angle, whereas with an asym, you will be reaching off into oblivion while your fleet sails away on you. Changing sails at that point could disrupt the boat enough to stop you dead. Either way, you are going to be tail end charlie!
There are other things you can do to help your light air performance that don't cost much. Simple things like a clean, smooth bottom are critical, particularly the foils. If you have a fixed blade prop, consider looking for a used folding one. A fixed prop is the biggest thing that will kill your light air performance. If you have a folding prop, are you sure it is folding? if it is a Martec or something similar where the blades are not geared, and the prop stops in the horizontal position, the bottom blade will drop down and cause drag because you are not moving fast enough for the water flow to close it. When I raced on a boat with one of those we marked the prop shaft where the blades would be aligned vertically. When we shut the engine off before the start, one of the crew would go down and turn the shaft to the marks to make sure the prop closes.