As much as I loved our Vanguard when we owned her, frankly it drives me crazy to see the reality of these boats so distorted by time. To correct some of your assumptions about the Vanguard from someone who actually owned and actually sailed Vanguards pretty extensively:
It is a mistake to say that Vanguards were built like a tank. The glass work on these boats was very sloppy and was just not all that heavy even when compared to newer designs and there was almost no internal framing. While these were moderately heavy boats overall for their waterline length, they were not especially heavy for a 32'6" boat. The excess weight was not in the laminate and the engineering was so poor that the weight did not produce a particularly strong boat.
Our Vanguard clipped a rock and we could never get it repaired correctly because the lay-up was so poor. We would ground out a spot looking for solid laminate and the hole would grow and grow and grow, still no solid lay-up. Our Vanguard evetually sank and now sits on the bottom of the East River but that is another story altogether.
Our Vanguard did have balsa cored decks (at least in the foredeck where we added a bigger chainpipe and vent), with plywood only at the reinforced areas for cleats
. That was already standard construction.
These boats were not full keels by any stretch of the imagination. The forefoot was cut away and the rudder post raked to the point that the keel was shorter on the bottom and had less area than the fin keel on a Cal 34 of that era. (In those days we referred to it as a fin keel with an attached rudder but that seems unpopular today) But what it meant is that these boat did not track worth a darn and were a real bear in heavy going.
Angle of vanishing stability is a product of many things, but except for the high freeboard and cabin on the Vanguard, there is little which should make you expect that they had had a large angle of vanishing stability. In terms of factors negatively affecting vanishing stability, Vanguards had a pretty wide beam for a boat of that era (and some of the immediately following eras) with the beam carried way out towards the very ends of the boat, were built with 500 lbs less ballast than the design or literature called for (confirmed by Phil Rhodes himself when we had ours), and shoal draft.
There is very little that is leisurely about sailing a Vanguard except their speed through the water. They were designed with minimal stability so that they are sailed on their ear in order to stretch thier water-line lengths. They were sailed at huge heel angles which with thier offset companionways could mean a lot of water down below in a knockdown and a lot of weather helm.
In any event, I am not sure why you think that the Tartan 30 is too small. The T-30 has a larger interior and cockpit, and a longer water line
. It only has a slightly smaller lazarette and a little less deck space aft. I would take a decently maintained Tartan 30 offshore any day of the week over a Vanguard in terms of ease of handling, safety, build quality and comfort. But that is just based on my experience sailing and working on both these boats.