For a non-racing glider pilot, what is the best use of a limitedsafety budget?

Too little information to give a good answer.

1. Parachute is first, should have one before you climb in any single seater.

Transponder and Flarm depend on density of glider and power traffic. High glider traffic and low power traffic favors Flarm. High power traffic, especially commercial with TCAS or radar services favor transponder first. If you have both high glider and high power get both.

Tim

Without a doubt more flight time! Being intimately familiar in a sensory perspective with your bird goes further than any periferal item as far as safety is concerned.