Va as one of the few aircraft I can recall which specify Va as a function of aircraft weight.
Actually, not quite correct.
Va probably is the most misunderstood parameter in the line pilot world. The basis of Va is control surface and related stuff strength. At the minimum value which the OEM may elect to use for design, the stall line will intersect with the limit load factor for the aircraft's design. If the OEM chooses a higher speed for Va the stall will be rather somewhat above the limit load factor and the risks of significant structural problems (of the sudden kind) become a tad worrying.
There are useful Va descriptions in PPRuNe (see posts by folks such as zzuf and djpil - both of these guys I know well and they know their stuff). Another, reasonably simplified story which you might find useful, is given in a thread at Bob Tait's theory website via the following link -
Bob Tait's Aviation Theory School - Maneuvering Speed with weight - Bob Tait's Aviation Theory School Forums
Eventually, the Vo limitation will overtake Va for pilot thinking and much of the problem associated with Va misinterpretation and misunderstanding will fade into the sunset. The main thing is to disabuse yourself of the idea that Va is where you can do heroic things with the stick ....
The main worry with old aircraft, especially in the GA environment where things go on without much oversight, relates to structural fatigue. This is a microscopic metal deterioration which leads to an eventual situation where the tin bits can fail during quite sedate flying, much to the short-lived surprise of the pilot at the time. One of the reasons for structural life limited restrictions and SSIP programs.